FUEL  ECONOMY  AND  CO2  RECORDERS 


McGraw-Hill  BoqkGompany 


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FUEL  ECONOMY  AND  CO2 
RECORDERS 

ENGINEERS'  STUDY  COURSE  FEOM  POWER 

A  PRACTICAL  MANUAL  DEALING  CHIEFLY  WITH  THE 

HEAT  LOSSES  IN  BOILERS  AND  THE  PRINCIPLE, 

OPERATION  AND  CARE  OF  CO,  RECORDERS 

AN  UNDERSTANDABLE  TREATMENT  OF 

COMBUSTION,  COAL  ANALYSIS,  FLUE  GAS  ANALYSIS.  BEAT  LOSSES  IN 
FLUE  GASES.  DRAFT.  CHIMNEY  DESIGN.  EVAPORATION.  BOIL- 
ER EFFICIENCY,  HEAT  BALANCE,  FEEDWATER  TREAT- 
MENT AND  COt  RECORDERS  AND  THEIR  TROUBLES 


BY 

A.  R.  MAUJER 

AND 

CHARLES  H.  BROMLEY 

OF  THK  EDITORIAL  STAFF  OF  POWKB 


FIRST  EDITION 
FOURTH  IMPRESSION 


McGRAW-HLLL  BOOK  COMPANY,  INC. 
239  WEST  39TH  STREET,  NEW  YORK 

6  BOUVERIE  STREET.  LONDON.  E,  a 

1914 


I 


1914,  ar  THE 
HILL  BOOK  GOUT 


PREFACE 

There  is,  perhaps,  no  subject  in  need  of  more  universal  attention 
among  power-plant  engineers  than  that  of  the  economical  use  of 
fuel  under  boilers.  Happfly  the  subject  is  getting  such  attention 
more  and  more  as  its  importance  is  realized. 

The  cost  of  fuel  in  most  plants  is  between  60  and  70  per  cent 
of  the  total  cost  of  power.  When  it  is  realized  further  that  due 
to  too  much  excess  air,  improper  furnace  design  and,  above  all, 
careless  and  ignorant  attendance,  as  much  as  twenty-five  and  more 
per  cent,  is  needlessly  wasted  in  most  plants,  the  reasons  for  such 
activity  as  is  now  displayed  are  manifest 

It  may  be  correctly  stated  that  the  average  power-plant  engineer 
has  had  but  few  persons  or  papers  to  point  out  to  him,  in  kis  mm 
language,  the  causes  of  waste  in  the  boiler  room.  Combustion 
to  him,  until  recently,  meant  maintaining  a  fire  hot  enough  to 
keep  the  steam  gage  indicating  the  correct  pressure.  The  chem- 
istry of  the  process  and  of  the  means  for  detecting  the  degree  of 
perfection  of  combustion  were  matters  for  others  to  consider — 
others  who  were  fortunate  enough  to  possess  the  education  to 
understand  the  terms  and  technical  "mysteries"  dealt  with. 

When  preparing  the  lessons  on  combustion  which  first  appeared 
in  the  Engineer's  Study  Course  from  POWER  and  which  make  up 
the  largest  pan  of  this  book,  the  aim  was  to  present  the  subjects 
treated  of  in  a  manner  easily  understandable  to  the  engineers  and 
firemen  who  have  to  do  with  the  final  use  of  the  fuel  and  on  whom 
depend  how  economically  it  will  be  used. 

THE  AUTHORS. 

J*tu,  1914. 


331181 


CONTENTS 

PAGB 

PREFACE    v 

CHAPTER  I 

PRINCIPLES  OF  COMBUSTION i 

Chemical  Reactions  in  Combustion I 

Carbon 4 

Hydrogen 5 

Sulphur 5 

Moisture,  Ash,  etc 6 

Air 7 

Measurement  of  Heat 9 

Combining  Weights  of  Elements 12 

Combustion  of  Carbon 12 

Combustion  of  Hydrogen 15 

Air  Required  for  Combustion 1 6 

CHAPTER  II 

ANALYSIS  OF  COAL 22 

Ultimate  Analysis 22 

Proximate  Analysis 23 

Sampling  Coal 24 

Apparatus  Required  for  Proximate  Analysis 26 

Making  the  Analysis 35 

Estimating  Heat  Value  of  Fuel 40 

Coal  Calorimeter 40 

Heat  Value  by  Calculation 42 

Heat  Value  by  Proximate  Analysis 44 

Heat  Value  from  Chart 45 

CHAPTER  III 

FLUE  GAS  ANALYSIS 49 

Excess  Air  Necessary 49 

Estimating  Air  Supplied 50 

Simplicity  of  Flue  Gas  Analysis 51 

vii 


viii  CONTENTS 

PAGE 

Apparatus  Required 51 

Unpacking  and  Assembling  Apparatus 52 

Loading  Apparatus ...  57 

Emptying  Pipettes 58 

Preparing  for  an  Analysis 58 

Effect  of  Temperature  and  Pressure 60 

Testing  for  CO2 63 

Checking  Results 64 

Testing  for  Oxygen 65 

Testing  for  CO 65 

Solution  for  COS 66 

Solution  for  Oxygen 67 

Solution  for  CO 67 

Taking  the  Sample 68 

Care  of  Apparatus 71 

CHAPTER  IV 

HEAT  LOST  IN  FLUE  GASES 72 

Heat  Lost  up  the  Chimney 72 

Specific  Heat.     ...            72 

Estimating  Heat  Lost  in  Flue  Gases 73 

Weight  of  Gases  per  Pound  of  Fuel 74 

Estimating  Total  Carbon  in  Coal 74 

Estimating  Nitrogen 76 

Ratio  of  Air  Required  to  Air  Supplied 78 

Measuring  Flue-gas  Temperature 79 

Practice  Problems 8o 

CHAPTER  V 

DRAFT  AND  ITS  MEASUREMENT 86 

Natural  Draft 86 

Absolute  Temperature 87 

Principle  of  Draft    ...            89 

CHAPTER  VI 

CHIMNEY  DESIGN 94 

Estimating  Draft  Required      .      .            96 

Draft  for  Various  Coals  and  Combustion  Rates 97 

Height  of  Chimney 99 

Diameter  of  Chimney IO1 

Practice  Problems    .           IO1 


CONTENTS  ix 

CHAPTER  VII 

PAGE 

EVAPORATION 104 

Water 104 

Boiling  Temperature 104 

Evaporation 106 

Latent  Heat 106 

Steam  Tables      .            109 

Gage  and  Absolute  Pressure ..no 

Properties  of  Saturated  Steam 112 

Heat  of  the  Liquid 114 

Total  Heat  in  Steam 114 

Equivalent  Evaporation .      .      .  115 

Boiler  Horsepower 118 

Quality  of  Steam 119 

Practice  Problems 121 

Steam  Calorimeters 122 

CHAPTER  VIII 

BOILER  EFFICIENCY 129 

Test  Apparatus  for  Calculating  Efficiency 131 

Weighing  Feedwater 131 

Object  of  Boiler  Test 134 

Duration  of  Test 136 

Starting  and  Stopping  Test 136 

Test  Report 137 

Analysis  of  Ash  and  Refuse 142 

Heat  Value  of  Coal 143 

Moisture  in  Steam 144 

CHAPTER  IX 

HEAT  BALANCE 148 

Object  of  Heat  Balance 148 

Itemized  Statement  of  Heat  Losses .      .  149 

Calculating  Hydrogen  in  Coal 150 

Calculating  Heat  Carried  Away  in  Gases 152 

Calculating  Heat  Lost  by  Incomplete  Combustion        .      .      .  153 

Efficiency  of  the  Boiler  and  Grate 153 

CHAPTER  X 

FEEDWATER  TREATMENT 155 

Common  Impurities 156 


x  CONTENTS 

PAGE 

Calcium  Carbonate 156 

Magnesium  Carbonate 159 

Calcium  Sulphate 160 

Magnesium  Sulphate 160 

Methods  of  Treatment 161 

Treatment  of  Carbonates 162 

Treatment  of  Sulphates 163 

Test  Apparatus 163 

Copper  Water  Bath 164 

Measuring  Flask 164 

Burette 165 

Indicators 166 

Hydrochloric  Acid  Solution 166 

Collecting  Sample 167 

Test  for  Alkalinity 167 

Temporary  Hardness 168 

Test  for  Acidity 168 

Permanent  Hardness 169 

Treatment  for  Sulphates 1 70 

Testing  Treated  Waters 171 

Scale  Remedies 172 

* 

CHAPTER  XI 

CO2  RECORDERS 175 

How  a  CO 2  Recorder  Works 175 

Absorption  of  Gas  by  Caustic  Potash 176 

Essentials  of  a  CO2  Recorder 178 

CO2  Recorder  Troubles 180 

Leaks  in  Gas  Sample  Pipe 180 

Interval  between  Renewals  of  Solution 180 

Proper  Strength  of  Solution 181 

Use  of  Sample  Collectors 181 

Single  and  Multiple  Recorders 182 

Caring  for  the  Recorder 182 

Correct  Location  for  Sample  Pipe 183 

Air  Leaks 183 

Filter  Troubles 184 

The  COj  Chart 184 

INDEX 187 


FUEL  ECONOMY  AND 
CO2  RECORDERS 

CHAPTER  I 
PRINCIPLES  OF  COMBUSTION 

Many  believe  that  to  understand  combustion  and  other  matters, 
such  as  flue-gas  analysis,  it  is  necessary  to  have  a  good  knowledge 
of  chemistry.  This  is  not  so.  However,  it  is  easiest  as  one  goes 
along  to  have  a  working  idea  of  a  few  simple  technical  terms. 
Therefore,  when  you  come  to  paragraphs  dealing  with  dry 
definitions  do  not  shy  around  them  but  wade  through.  They  are 
there  for  a  purpose  and  you  will  be  paid  for  your  trouble. 

When  an  engineer  talks  about  combustion  he  means  the  burning 
of  such  fuels  as  wood,  peat,  the  various  grades  of  coal,  such  as 
lignites,  bituminous  coals  and  anthracite;  coke,  oil,  gases  and 
such  byproduct  fuels  as  tar,  bagasse,  which  is  sugar  cane  after  the 
sugar  has  been  extracted,  spent  tan  bark,  corn  and  corn  cobs,  etc. 

The  principal  element  in  all  of  these  fuels  is  carbon  which,  by 
the  way,  is  one  of  the  most  widely  distributed  elements  in  nature. 
The  diamond  is  pure  carbon;  sugar  contains  a  large  proportion  of 
it;  coke  is  almost  pure  carbon;  paper  contains  carbon,  so  does  ink; 
plants,  trees,  etc.,  are  composed  largely  of  carbon,  and  even  the 
human  being  has  a  large  percentage  of  this  element  in  his 
makeup. 

It  is  now  important  to  know  what  an  element  is.  Any  gas, 
liquid  or  solid  which  cannot  be  changed  by  some  process  or  other 
which  causes  chemical  change,  into  two  or  more  substances  of 
distinctly  separate  natures  is  called  an  element.  On  the  other 
hand,  a  gas,  liquid  or  solid  which  can  be  changed  is  called  a  com- 


FUEL  ECONOMY  AND  CO2  RECORDERS 


Col.  i 


TABLE  I.— COMBUSTION  DATA 
Col.  2  Col.  3 


Col.  4 


Name  of  Element 

Symbol  of 
Element 

Combining 
Weight 

Combustion 
Formula 

Carbon 

c 

12 

c  +  o  =  co 

C  +  20  =  CO2 

CO  +    O  =  CO2 

Hydrogen 

H 

I 

2H  +    O  =  H2O 

Sulphur 

S 

32 

S  +  2O  =  S02 

s  +  3o  =  sOs 

Oxygen 

o 

16 

Nitrogen 

N 

id. 

Col.  5 


Col.  6 


Col.  7 


Col.  8 


Compound  Formed 

Heat  Liber- 
ated. B.t.u. 
per  Ib.  of 
Combustible 

Pounds  of  Oxy- 
gen Required 
per  Ib.  of 
Combustible 

Pounds  of  Air 
Required  per 
Ib.  of 
Combustible 

Carbon  Monoxide  (Incom- 

4,450 

ll 

5-76 

plete  Combustion) 

Carbon  Dioxide  (Complete 

14,600 

a| 

11.52 

Combustion) 

Carbon  Dioxide 

4,350 

1 

2-47 

Water 

62,000 

8 

34.56 

Sulphur  Dioxide 

Sulphur  Trioxide 

pound.  To  illustrate,  pure  iron  is  an  element  because  there  is  no 
way  to  convert  it  or  "  break  it  up  "  into  anything  but  iron.  Iron- 
rust,  however,  is  a  compound,  because  it  is  a  chemical  combina- 
tion of  iron  and  oxygen  and  can  be  divided  by  a  chemical  process 
into  iron  and  oxygen.  Water  is  a  compound  because  it  can  be 
divided  by  intense  heat  or  by  electricity  into  two  gases,  hydrogen 
and  oxygen. 

These  two  gases,  hydrogen  and  oxygen,  are  elements  because 
it  is  impossible  to  convert  them  into  anything  but  what  they  are. 
They  may,  however,  be  reunited  chemically  with  other  elements 
or  with  compounds  and  form  many  different  substances.  Air 
is  neither  an  element  nor  a  compound.  It  is  simply  a  mixture 


PRINCIPLES  OF  COMBUSTION  3 

of  elements,  mainly  oxygen  and  nitrogen,  which  may  be  separated 
without  any  chemical  change  taking  place  in  the  mixture. 

Although  there  are  thousands  of  chemical  compounds,  there  are 
but  79  known  elements  and  nearly  half  of  these  are  exceedingly 
rare  ones.  In  the  study  of  combustion,  we  deal  with  but  the 
five  showrn  in  Table  I. 

There  are  two  kinds  of  changes  possible  in  nature,  physical 
changes  and  chemical  changes.  A  physical  change  is  one  that 
affects  the  form  of  a  substance  but  not  its  character,  while  a 
chemical  change  usually  affects  both  form  and  character.  Two 
examples  of  physical  changes  are  the  freezing  of  water  to  form 
ice  and  the  heating  of  water  to  form  steam.  While  each  of  these 
causes  the  form  of  the  water  to  change  (in  one  case  to  a  solid;  in 
the  other  to  a  vapor)  the  composition  remains  exactly  the  same. 
If  you  take  a  lump  of  coal  and  hammer  it  into  a  powder  you  have 
caused  only  a  physical  change,  for  you  have  only  changed  the 
form  of  the  coal  from  a  lump  to  a  powder  which  is  simply  a  mass 
of  very  small  lumps  of  coal  having  the  same  characteristics  as  the 
original  big  lump.  But  if  you  burn  a  lump  of  coal,  it  gives  off 
light  and  heat  and  the  coal  changes  into  an  ash  and  some  in- 
visible gases.  This  is  a  chemical  change  because  the  nature  of 
the  substance  is  completely  altered.  First  you  had  coal,  composed 
of  a  large  proportion  of  carbon  and  small  proportions  of  other 
substances,  such  as  hydrogen,  sulphur,  etc.  After  the  change 
you  had  left  a  little  ash.  The  rest  of  the  coal  was  converted  into 
gases  and  these  passed  off  into  the  air. 

From  this,  then,  we  can  describe  combustion  as  a  chemical 
combination  of  one  or  a  number  of  combustibles  (such  as  those  in 
Table  I),  with  oxygen  (the  supporter  of  combustion),  when  light 
and  heat  are  produced. 

A  fact  which  is  very  fortunate  from  our  point  of  view  is  this: 
Chemical  elements  follow  exact  laws  when  they  enter  into 
chemical  combinations  with  each  other;  a  fixed  weight  of  one  ele- 
ment always  combines  with  a  fixed  weight  of  another  to  form  a 
given  compound.  Also,  a  definite  amount  of  heat  is  always 
created  when  a  given  combination  takes  place.  Thus,  when 


4         FUEL  ECONOMY  AND  CO2  RECORDERS 

hydrogen,  one  of  the  combustible  elements  of  many  fuels,  burns,  it 
always  requires  a  fixed  amount  of  oxygen;  it  always  causes  a 
certain  amount  of  heat,  and  it  always  results  in  a  certain  quantity 
of  the  product  of  its  combustion. 

CARBON 

Carbon  in  its  pure  state  is  a  solid,  such  as  graphite  and 
diamonds.  As  found  in  solid  fuels,  part  of  it  is  pure  and  part  is  in 
combination  with  hydrogen  forming  hydrogen-carbon  combina- 
tions which,  for  brevity,  are  spelled  and  pronounced  hydrocarbons. 
The  pure  carbon  part  of  a  fuel  is  usually  referred  to  as  "fixed 
carbon"  because  when  the  fuel  is  heated  the  hydorcarbons 
vaporize  and  pass  off  in  the  air,  the  same  as  water  in  a  sponge 
vaporizes  and  passes  off.  The  pure  carbon  remains  behind, 
consequently  we  say  it  is  " fixed." 

In  liquid  fuel,  such  as  crude  oil  or  any  of  the  products  of  crude 
oil,  such  as  kerosene  and  gasoline,  carbon  is  not  found  in  the  pure 
state  but  is  always  present  in  combinations  with  hydrogen  as 
hydrocarbons.  Carbon  exists  in  gaseous  fuels,  such  as  natural 
gas,  illuminating  gas,  blast-furnace  gas,  etc.,  but  only  in  com- 
bination with  either  hydrogen  or  oxygen  (principally  with  hy- 
drogen in  the  shape  of  hydrocarbons). 

When  carbon  burns  completely,  it  always  requires  a  certain 
amount  of  oxygen,  and  hence,  a  certain  amount  of  air,  because 
the  oxygen  is  supplied  by  the  air  and  the  proportion  of  oxygen 
found  in  the  air  is  the  same  in  New  York  as  it  is  in  Punxsutawney 
or  San  Francisco;  in  fact,  the  proportion  remains  the  same  the 
world  over.  You  may  supply  more  oxygen  by  supplying  more 
air  but  the  excess  will  not  be  used.  A  given  amount  of  carbon 
will  use  (or  combine  with)  only  so  much  oxygen,  never  any  more 
and  never  any  less. 

Did  you  notice  in  the  beginning  of  the  last  paragraph  that  it 
was  said  "when  carbon  burns  completely"?  Care  was  taken  to 
specify  complete  combustion  because  carbon  will  undergo  partial 
or  incomplete  combustion  when  conditions  are  not  right  for 


PRINCIPLES  OF  COMBUSTION  5 

complete  combustion.  But  this  need  not  worry  us,  because  this 
incomplete  combustion  also  follows  definite  laws.  A  certain 
amount  of  carbon  incompletely  burned  will  use  a  certain  amount 
of  air  every  time  and  will  give  up  a  certain  amount  of  heat  every 
time.  What  the  oxygen  or  air  requirement  is  in  each  case  and 
what  the  amount  of  heat  is  created  will  be  taken  up  later.  Just 
now  we  will  talk  about  some  of  the  other  elements. 

HYDROGEN 

Pure  hydrogen  is  a  colorless  and  odorless  gas.  It  exists  in  coal 
in  combination  with  carbon,  forming  the  hydrocarbons  mentioned 
before.  These  hydrocarbons  form  the  principal  part  of  the 
volatile  matter  in  coal.  When  a  coal  is  heated  to  a  certain  tem- 
perature, certain  quantities  of  vapors  or  gases  are  given  off, 
depending  on  the  nature  of  the  coal.  With  bituminous  or  "soft" 
coals,  large  quantities  are  given  off;  with  anthracite  or  "hard" 
coals  only  small  quantities  are  given  off.  These  vapors  or  gases 
are  known  as  the  volatile  matter  of  the  coal.  Hydrogen  is  like- 
wise found  in  a  combined  state  in  the  liquid  fuels.  In  gaseous 
fuels  it  exists  in  both  the  free  and  the  combined  state. 

When  hydrogen  burns,  it  burns  completely;  there  is  no  part  or 
half-way  process  with  it  as  is  the  case  with  carbon.  Hydrogen 
produces  intense  heat  and  as  a  fuel  it  has  great  value. 

SULPHUR 

Sulphur  in  its  pure  state  is  a  yellow  solid  substance  which 
burns  very  easily  and  forms  a  disagreeable  smoke.  It  exists  to 
some  extent  in  practically  all  coals  and  fuel  oils.  It  is  undesirable 
in  fuel  because  its  heat  value  is  very  small  and  because  it  tends 
to  form  an  acid  which  quickly  corrodes  the  ironwork  of  flues  and 
chimneys.  Sulphur  also  increases  the  clinkering  properties  of 
the  coal.  Ordinarily  the  amount  of  sulphur  found  in  coal  and 
oil  is  small,  and  hence,  because  its  heat  value  is  low,  we  can 
easily  afford  to  ignore  it  in  our  calculations.  It  is  well  to  bear 


6         FUEL  ECONOMY  AND  CO2  RECORDERS 

in  mind,  however,  that  the  less  sulphur  a  fuel  contains  the  more 
desirable  it  is. 

MOISTURE,  ASH,  ETC. 

In  addition  to  the  elements  just  mentioned,  all  solid  fuels 
contain  water,  ash  and  a  few  other  impurities.  The  water  is 
usually  referred  to  as  moisture.  This  water  cannot  be  squeezed 
out  like  water  from  a  sponge,  but  it  can  practically  all  be  dried 
out  from  coal  simply  by  heating  the  coal  for  a  certain  length  of 
time.  In  oil  fuel,  which  also  contains  moisture,  most  of  the  water 
will  settle  out  when  the  oil  is  allowed  to  stand  for  a  sufficient  time. 

The  amount  of  moisture  which  a  coal  contains  depends  almost 
entirely  upon  the  nature  of  the  coal.  Some  coals  are  more  sponge- 
like  than  others;  that  is,  they  have  greater  capacity  for  holding 
water  than  others.  The  amount  of  ash  or  unburnable  solid 
material  in  coal  also  varies  greatly  with  the  kind  of  coal,  and  some- 
times the  same  kind  of  coal  will  run  very  unevenly  in  this  respect. 
As  ash  and  moisture  do  not  create  heat,  naturally,  the  less  of 
these  a  fuel  contains  the  better  it  is. 

In  addition  to  the  ash  and  moisture,  coal  contains  a  few  other 
impurities,  principally  oxygen  and  nitrogen.  The  latter  need 
not  worry  us  in  the  least  because  the  amount  of  it  is  small  and  it 
has  but  slight  effect  on  the  results  anyhow.  The  oxygen  con- 
tained in  coal  sometimes  runs  rather  large  in  quantity  and  hence 
it  is  important  to  know  about  it,  although  in  our  ordinary  work 
in  boiler-room  economy  we  can  afford  to  forget  about  it,  and  we 
will,  later  on,  when  we  "get  down  to  cases."  But  it  is  a  good 
idea  to  get  a  fair  understanding  of  the  whole  story  so  that  when 
we  read  technical  articles  and  reports  we  will  have  some  idea  of 
what  they  are  all  about. 

Even  the  scientists  are  not  certain  as  to  exactly  what  form 
oxygen  exists  in  coal.  They  are  not  sure  whether  it  is  there  as  an 
element,  that  is,  as  free  or  uncombined  oxygen;  or  as  a  compound 
with  hydrogen  in  the  form  of  water  so  tightly  mixed  up  in  the  coal 
that  no  amount  of  heating,  short  of  burning,  will  drive  it  out 
like  ordinary  water;  or  whether  it  is  in  the  coal  in  some  com- 


PRINCIPLES  OF  COMBUSTION  7 

bination  with  carbon  as  carbon  dioxide  or  C02.  However,  it  is 
generally  believed,  and  always  assumed  that  the  oxygen  exists  in 
the  coal  as  a  compound  with  hydrogen  in  the  form  of  water. 
Hence,  when  an  analysis  of  a  coal  shows  that  it  contains  both 
oxygen  and  hydrogen,  only  part  of  the  hydrogen  is  considered  as 
available  for  combustion.  The  other  part  is  considered  as  being 
already  combined  chemically  with  the  oxygen  of  the  coal  in  the 
form  of  water,  H2O.  And,  as  water  is  noncombustible,  the 
hydrogen  thus  combined  is  useless  as  fuel.  Hence,  when  you  see 
the  term  "available  hydrogen"  in  a  report  of  a  coal  analysis, 
you  will  know  that  it  means,  not  all  the  hydrogen  found  in  the 
coal,  but  only  the  part  which  is  in  excess  of  the  amount  required 
by  the  oxygen  existing  in  the  coal  to  form  water. 

AIR 

Air  is  composed  of  the  gases,  oxygen  and  nitrogen,  and  very 
small  quantities  of  a  few  other  elements  and  a  few  compounds. 
The  oxygen  and  nitrogen  form  such  a  large  part  of  the  air  (99  per 
cent,  or  more)  that  for  all  practical  purposes  they  are  the  only 
constituents  to  be  considered.  As  found  in  the  air  they  are  both 
pure,  that  is,  uncombined  with  any  other  elements. 

Some  people  have  difficulty  in  realizing  that  a  gas  has  weight. 
They  think:  "You  never  could  weigh  a  gas;  it  is  too  light;  it 
would  not  stay  on  the  scale."  Consequently,  they  get  confused 
when  they  read  about  pounds  of  air  or  pounds  of  oxygen.  It  is 
really  easy  to  weigh  a  gas  if  you  have  a  good  strong  tank  or 
cylinder  and  a  pair  of  scales  that  are  very  sensitive  and  accurate. 
Suppose  you  wished  to  weigh  air,  for  instance.  Although  air  is 
not  a  simple  gas,  but  a  mixture  of  the  two  gases,  oxygen  and  ni- 
trogen, it  makes  no  difference,  the  action  is  the  same. 

Close  the  valve  on  the  tank,  put  the  tank  on  the  scale  and 
weigh  it.  We  know  that  the  tank  is  full  of  air  at  atmospheric 
pressure,  because  a  pressure  gage  attached  to  the  tank  would 
show  zero  pressure.  Now,  connect  a  good  vacuum  pump  to  the 
tank  and  pump  and  pump  and  pump  until  the  vacuum  gage 


8 


FUEL  ECONOMY  AND  CO,  RECORDERS 


shows  as  near  30  in.  of  vacuum  as  you  can  get  it  to  show.  Then 
weigh  the  tank  again.  This  time  the  weight  will  be  less,  proving 
that  air  has  weight.  If  the  temperature  of  the  air  was  60  deg., 
if  the  tank  had  a  capacity  of  5  cu.  ft.  and  if  it  weighed  75  Ib.  the 
first  time,  it  would  weigh  something  like  74.618  Ib.  the  second 


FIG.  i. — Experiment  to  show  that  air  has  weight. 

time,  showing  that  the  5  cu.  ft.  of  air  pumped  out  weighed  0.382 
Ib.  or  that  air  at  60  deg.  temperature  and  atmospheric  pressure 

•     T-_ 


weighs 


0.382 
5 


0.0764  Ib.  per  cubic  foot. 


(By  the  way,  it  was  not  necessary  to  close  the  valve  on  the  tank 
for  the  first  weighing.  But  this  is  another  story  to  be  taken  up 
later.) 

You  will  notice  that  the  temperature  of  the  air  when  the  weigh- 
ing took  place  was  specified.  This  was  done  because  air  (or  any 
gas)  is  a  very  elastic  fluid  and  expands  and  contracts  very  easily 
by  being  heated  and  cooled;  hence  its  weight  per  cubic  foot 
changes  with  change  of  temperature;  that  is,  unless  it  happens 
to  be  inclosed  in  some  vessel  that  will  not  let  it  expand.  Then  it 
is  not  the  volume  nor  the  weight  that  changes,  but  the  pressure. 


PRINCIPLES  OF  COMBUSTION  9 

If  you  think  of  a  gas  as  a  very  light  fluid  it  is  easy  to  realize 
that  it  has  weight  just  the  same  as  any  other  fluid,  such  as  water. 

By  volume,  air  is  composed  of  21  per  cent,  oxygen  and  79  per 
cent,  nitrogen.  That  is,  out  of  every  100  cu.  ft.  of  air,  21  cu.  ft. 
is  oxygen  and  79  nitrogen.  By  weight,  air  is  composed  of  23.15 
per  cent,  oxygen  and  76.85  per  cent,  nitrogen.  That  is,  out  of 
every  100  Ib.  of  air,  23.15  Ib.  is  oxygen  and  76.85  Ib.  nitrogen. 

MEASUREMENT  OF  HEAT 

Now,  before  we  take  up  combustion,  coal  analysis  and  similar 
subjects,  we  ought  to  get  a  good  working  idea  about  how  heat  is 
measured  because  it  is  necessary  to  measure  the  heat  generated 
and  absorbed  so  as  to  know  what  results  we  are  getting. 

Heat  is  measured  by  its  intensity  or  degree  and  by  its  amount 
or  quantity.  If  you  lighted  an  ordinary  match  and  held  it  so  the 
flame  struck  the  business  end  of  a  quick-acting  thermometer 
that  could  stand  the  treatment,  the  thermometer  would  indicate 
a  certain  temperature,  let  us  say  400  deg.  Then,  if  you  lighted 
two  matches  and  held  them  so  that  both  flames  struck  the  ther- 
mometer it  might  astonish  you  when  you  found  the  thermometer 
showed  only  the  same  temperature  as  before.  You  could  easily 
see  that  there  was  twice  as  much  flame  and  it  stands  to  reason 
that  there  was  twice  as  much  heat  because  you  were  burning 
two  matches  instead  of  one  and  two  matches  have  twice  as  much 
wood  as  one.  Then,  why  was  not  the  temperature  twice  as  great? 
Because  the  temperature  or  the  intensity  of  heat  depends  upon 
the  nature  of  the  fuel  and  the  way  it  is  burned  while  the  amount 
burned  determines  the  quantity  of  heat  created.  The  fire  under  a 
5o-hp.  boiler  may  be  just  as  "hot,"  the  temperature  may  be  just 
as  high,  as  the  one  under  a  5oo-hp.  boiler,  yet  it  does  not  do  as 
much  work,  that  is,  heat  as  much  water,  because  it  does  not  burn 
as  much  fuel  and  consequently  does  not  generate  as  great  a  quan- 
tity of  heat. 

Now,  it  is  seldom  possible  to  measure  the  quantity  of  heat 
direct,  but  it  is  quite  easy  to  calculate  the  quantity  when  the 


10 


FUEL  ECONOMY  AND  CO2  RECORDERS 


temperature  and  a  few  other  factors  are  known.  This  is  true 
because  heat  acts  according  to  fixed  laws,  the  same  as  every- 
thing else  in  this  world.  And  when  you  once  understand  those 
laws  it  is  easy  to  figure  out  what  will  happen  when  certain  con- 
ditions prevail. 


FIG.  2. — Experiment  to  show  that  a  flame's  temperature  is  independent  of  its 


size. 


DEFINITION  OF  B.T.U. 

The  thermometer  measures  temperature  or  heat  intensity  and 
the  unit  of  temperature  is  the  degree.  According  to  the  Fahren- 
heit scale,  which  is  the  one  commonly  used  in  this  country, 


PRINCIPLES  OF  COMBUSTION  II 

melting  ice  has  a  temperature  of  32  deg.  and  boiling  water  a 
temperature  of  212  deg. 

The  unit  of  heat  quantity  commonly  used  is  the  British  thermal 
unit  or  the  B.t.u.,  as  it  is  usually  written  and  pronounced.  It 
gets  its  name  from  the  fact  that  British  scientists  established  it  or 
used  it  first  and  the  word  thermal  means  heat  or  warmth.  An- 
other way  of  expressing  it  would  be,  British  unit  of  heat  measure- 
ment. In  fact,  we  often  use  the  term  heat  unit  when  we  really 
mean  B.t.u. 

One  B.t.u.  is  the  quantity  of  heat  required  to  raise  the  tem- 
perature of  i  Ib.  of  water  i  deg.1  As  a  gallon  of  water  weighs  8J 
lb.,  it  requires  8j  B.t.u.  to  raise  the  temperature  of  i  gallon  i  deg., 
or  i6f  B.t.u.  to  raise  the  temperature  2  deg.,  and  so  on. 

Thus,  when  a  given  coal  is  said  to  have  a  heat  value  of  13,800 
B.t.u.  per  pound,  it  is  meant  that  if  all  the  heat  caused  by  the 
complete  combustion  of  i  lb.  of  that  coal  could  be  transmitted 
to  13,800  lb.  of  water  it  would  raise  the  temperature  of  that 
water  i  deg.  Or,  if  all  the  heat  could  be  transmitted  to,  say 
138  lb.  of  water,  it  would  raise  the  temperature  of  that  water 
just  100  deg.,  because 

138  X  100  =  13,800 

The  pounds  of  water  heated  multiplied  by  the  number  of  degrees 
the  temperature  has  been  raised  equals  the  number  of  B.t.u. 

Indeed,  the  standard  method  of  finding  the  heat  value  of  a 
fuel  is  to  burn  a  small  sample  of  it  in  a  tight  steel  bomb  under 
water.  The  heat  caused  by  the  burning  of  the  sample  is  then  all 
absorbed  by  the  water  and  by  multiplying  the  weight  of  the 

1  This  is  only  approximately  true.  It  takes  a  different  amount  of  heat  to 
raise  a  pound  of  water  from  32  deg.  to  33  deg.  than  it  does  to  raise  it 
from  100  deg.  to  101  deg.,  or  from  211  deg.  to  212  deg.  The  B.  t.u., therefore, 
is  variously  defined  as  the  amount  of  heat  necessary  to  raise  a  pound  of 
water  i  deg.  at  its  temperature  of  maximum  density,  about  39  deg.;  or,  at 
some  arbitrary  temperature,  60  or  62  deg.,  because  that  is  assumed  to  be  the 
average  temperature  of  the  surrounding  air  when  experiments  to  determine 
the  amount  of  heat  are  made;  or  Ti^  of  the  amount  of  heat  required  to  raise 
a  pound  of  water  from  32  to  212  deg.  (the  average  amount  of  heat  per  degree). 
The  latter  definition  is  finding  the  most  favor. 


12        FUEL  ECONOMY  AND  CO2  RECORDERS 

water  by  its  rise  in  temperature  and  dividing  by  the  weight 
of  the  sample,  the  heat  value  of  the  coal  is  calculated  direct  in 
B.t.u.  per  pound.  Thus,  if  we  burned  a  small  sample  weighing  one- 
five-hundredth  of  a  pound  in  a  bomb  immersed  in  5  Ib.  of  water 
and  if  the  temperature  of  that  water  increased  from,  say,  70.4  deg. 
to  75.92  deg.,  a  rise  of  5.52  deg.,  the  heat  value  of  the  coal  would  be 

- — —  =  13,800  B.t.u.  per  pound. 
0.002 

COMBINING  WEIGHTS  OF  ELEMENTS 

Whenever  a  chemical  action,  such  as  combustion,  takes  place, 
the  elements  or  compounds  always  combine  in  fixed  proportions 
by  weight.  Because  of  this  fact  we  are  able  to  use  Col.  3  in  Table 
I,  which  gives  the  combining  weights  of  the  various  elements. 
Whenever  two  or  more  elements  combine  they  do  so  either  in 
direct  proportion  to  the  numbers  shown  in  Col.  3  or  in  some  mul- 
tiple of  those  numbers.  The  exact  manner  in  which  they  combine 
is  shown  by  the  formulas  in  Col.  4.  Thus,  when  carbon  combines 
with  other  elements  it  always  combines  in  weights  of  12  or  some 
multiple  of  12,  such  as  24,  36,  48,  etc.,  depending  on  the  for- 
mula. When  oxygen  combines  it  does  so  in  weights  of  16  or 
multiples  of  16.  And  so  with  all  other  elements,  they  combine 
according  to  their  combining  weights  or  atomic  weights  as  the 
chemist  usually  calls  them. 

COMBUSTION  OF  CARBON 

Carbon  has  two  ways  of  combining  with  oxygen.  One  is  called 
complete  combustion  and  the  other  incomplete  combustion. 
Whether  combustion  is  complete  or  incomplete  depends  upon 
conditions.  If  sufficient  air  is  supplied  to  every  particle  of  the 
carbon,  combustion  will  be  complete;  if  not,  some  of  the  carbon 
will  be  only  partially  burned. 

Taking  up  incomplete  combustion  first,  the  formula  in  Col.  4  is 

C  +  O  =  CO 


PRINCIPLES  OF  COMBUSTION  13 

This  means  that  the  carbon  combines  with  the  oxygen  in  the  pro- 
portion by  weight  of  12  to  16,  because  those  are  the  combining 
weights  of  the  two  elements.  This  reduces  to  i  to  i^.  Hence, 
for  every  pound  of  carbon  incompletely  burned  ij  Ib.  of  oxygen 
are  required.  If  27  Ib.  of  carbon  were  incompletely  burned  the 
amount  of  oxygen  used  would  be  36  Ib.,  because  the  proportion 
of  27  to  36  is  the  same  as  12  to  16  or  i  to  i  J.  The  figuring  is  just 
the  same  for  all  other  quantities  of  carbon  no  matter  whether  the 
amount  is  a  fraction  of  an  ounce  or  thousands  of  tons. 

The  product  of  the  incomplete  combustion  of  carbon  is  a  gas 
called  carbon  monoxide  and  its  chemical  symbol  is  CO. 

The  name  monoxide  is  one  of  those  built-up  words  from  mono, 
meaning  one  or  one  part,  and  oxide,  meaning  the  chemical  union 
of  oxygen  with  some  other  substance.  Thus,  carbon  monoxide 
means  one  part  of  oxygen  united  with  carbon.  When  the  number 
of  parts  of  the  other  element  is  not  stated  it  is  always  taken  as 
one.  Hence,  the  exact  meaning  of  carbon  monoxide  is  one  part 
of  carbon  united  with  one  part  of  oxygen. 

To  calculate  the  amount  in  pounds  of  the  CO  formed  it  is  only 
necessary  to  add  the  weight  of  the  carbon  burned  and  the  weight 
of  the  oxygen  required  according  to  the  formula;  the  result  is 
the  weight  of  the  carbon  monoxide.  What  the  volume  of  this 
gas  is  depends  upon  the  temperature  as  has  been  explained. 

Thus,  if  5  Ib.  of  carbon  are  incompletely  burned  the  weight  of 
CO  formed  is 

Weight  of  carbon 5    Ib. 

Weight  of  oxygen  required  5  X  15 6f  Ib. 


Weight  of  carbon  monoxide  formed nf  Ib. 

This  carbon  monoxide  is  a  combustible  gas  and  if  supplied  with 
air  so  that  it  can  unite  with  the  required  amount  of  oxygen  it  will 
burn  when  heated  to  its  temperature  of  ignition.  Its  formula  is 

CO  +  O  =  CO2 


14        FUEL  ECONOMY  AND  CO2  RECORDERS 

This  means  that  the  CO  or  carbon  monoxide  combines  with 
oxygen  in  the  proportion  of 

C  +  O  to  O 

12  +  16  to  16  =  28  to  16 

or  i  to  Tg-fi  which  equals  i  to  T.  Thus,  for  every  pound  of  CO 
burned  %  of  a  pound  of  oxygen  is  required. 

The  product  of  the  combustion  of  CO  is  a  gas  called  carbon 
dioxide,  which  has  the  chemical  symbol  CO2. 

The  name  dioxide  is  built  up  in  a  manner  similar  to  monoxide, 
the  prefix  di  meaning  two  or  two  parts.  Thus,  carbon  dioxide 
means  one  part  of  carbon  combined  with  two  parts  of  oxygen. 
By  "parts"  it  must  be  remembered  we  mean  "chemical  parts," 
i.e.,  combining  weights  as  shown  in  Table  I  and  explained  before. 
The  weight  of  CO2  formed  by  the  combustion  of  CO  is  found  by 
adding  the  weight  of  CO  burned  to  the  amount  of  oxygen  required 
according  to  the  formula.  Thus,  if  6  Ib.  of  CO  were  burned  to 
CO2  the  weight  of  CO2  formed  would  be 

Weight  of  CO  burned 6    Ib. 

Weight  of  oxygen  required  6X7 37  Ib. 

Weight  of  carbon  dioxide  formed 97  Ib. 

If  sufficient  air  is  supplied  in  the  first  place  so  that  each  particle 
of  carbon  can  unite  with  all  the  oxygen  it  desires,  complete  com- 
bustion results,  the  formula  for  which  follows: 

C  +  2O  =  CO2 

This  means  that  the  carbon  unites  with  the  oxygen  in  the 
proportion  of 

C  +  2O  =  CO2 

12  +  2  (16)  =  44 

producing  J £  =  3!  Ib.  of  CO2  for  every  pound  of  carbon  burned. 
Every  pound  of  carbon  when  completely  burned  requires  1 1  =  i\ 
Ib.  of  oxygen. 


PRINCIPLES  OF  COMBUSTION  15 

COMBUSTION  OF  HYDROGEN 

When  carbon  is  burned,  part  of  it  may  be  burned  completely 
to  form  CC>2  and  the  rest  may  be  only  partly  burned  to  form  CO. 
This  is  not  true  of  hydrogen.  The  hydrogen  either  burns  com- 
pletely or  not  at  all.  Thus,  if  not  enough  air  is  supplied  for  a 
given  quantity  of  hydrogen,  part  of  the  hydrogen  (enough  to 
use  up  all  the  oxygen  in  the  air  supplied)  burns  completely  and 
the  balance  does  not  burn  at  all. 

The  formula  for  the  combustion  of  hydrogen  is 

2H  +  O  =  H2O 

According  to  Table  I,  Col.  3,  the  combining  weight  of  hydrogen 
is  i,  that  of  oxygen  16,  the  same  as  in  all  other  cases.  Thus, 
substituting  in  the  formula,  we  have 

2H  +  O  =  H2O 

2  (i)  +  16  =  18 

It  requires  then  l£-  =  8  Ib.  of  oxygen  for  the  complete  combus- 
tion of  every  pound  of  hydrogen  burned,  and  the  weight  of  the 
product  formed  is  ±£-  =  9  Ib. 

The  product  formed  by  the  combustion  of  hydrogen  is  water 
(H2O)  in  the  shape  of  highly  superheated  steam.  This  steam 
can  be  condensed  just  the  same  as  steam  made  directly  from 
water  can  be  condensed  back  into  water  again. 

Sulphur  burns  with  oxygen  and  forms  SO2  in  much  the  same 
way  that  carbon  burns  to  form  CO2.  The  formula  is 

S  +  2O  =  SO2 
32  +  2  (16)  =  64 

From  this  it  will  be  seen  that 

tf  -  •  i  A, 


1  6        FUEL  ECONOMY  AND  CO2  RECORDERS 

of  oxygen  is  required  for  the  combustion  of  every  pound  of  sulphur 
and  that 


of  sulphur  dioxide  are  formed. 

Sulphur  will  also  combine  according  to  this  formula 

S  +  30  =  S03 

Here  \  Ib.  more  of  oxygen  is  required  for  combustion.  These 
products  (SO2  and  SO3)  easily  combine  with  water  and  form  sul- 
phurous and  sulphuric  acid  as  follows: 

502  +  H20  =  H2SO3 

503  +  H2O  =  H2SO4 

These  acids  strongly  attack  iron  and  hence  do  injury  to  flues 
and  chimneys  made  of  that  material. 

As  pointed  out  previously,  the  heat  value  of  sulphur  is  so  low 
and  the  percentage  of  sulphur  found  in  the  average  grade  of  coal 
is  so  small  that  we  can  easily  afford  to  neglect  it  completely  in 
our  calculations. 

WEIGHT  OF  AIR  REQUIRED 

So  far  we  have  been  talking  about  and  figuring  for  the  quantity 
of  oxygen  required  for  the  combustion  of  the  various  elements. 

The  only  cheap  source  of  oxygen  for  the  purpose  of  combustion 
is  the  air,  which  is  free  for  everyone  to  use.  The  nitrogen  of  the 
air  is  an  incombustible  gas;  that  is,  it  will  not  burn  with  oxygen  no 
matter  how  much  it  is  heated,  neither  will  it  burn  with  any  of  the 
combustibles  of  the  fuels.  Hence,  it  is  entirely  useless  for  the 
purpose  of  combustion.  But,  there  is  no  economical  way  of 
separating  the  oxygen  from  the  nitrogen  and  as  they  are  thor- 
oughly mixed  together  we  must  supply  the  nitrogen  to  the  fire 
along  with  the  oxygen. 


PRINCIPLES  OF  COMBUSTION  17 

As  the  ratio  by  weight  of  nitrogen  to  oxygen  is  76.85  to  23.15, 
for  every  pound  of  oxygen  required  we  must  supply 


of  nitrogen  and  hence  for  every  pound  of  oxygen  required  we  must 
supply 

Oxygen  +  Nitrogen  =  Air 

i  +  3.32  =  4.32  Ib.  of  air 

Col.  8,  Table  I,  gives  the  pounds  of  air  required  per  pound  of 
combustible  in  Col.  4.  These  figures  may  be  used  to  shorten  the 
work  when  figuring  the  air  required. 

If,  instead  of  burning  just  a  single  combustible  element,  such  as 
carbon  or  hydrogen,  we  burn  a  fuel  containing  both  of  these  ele- 
ments, we  figure  the  oxygen  or  the  air  required  for  the  amount  of 
each  element  contained  in  i  Ib.  of  the  fuel  just  the  same  as 
though  that  element  was  the  only  one  under  consideration.  The 
sum  of  the  amounts  of  air  required  for  each  element  then  equals 
the  amount  of  air  required  per  pound  of  the  fuel  in  question. 

Thus,  if  we  had  a  coal  which  contained,  say  80  per  cent,  carbon; 
5  per  cent,  available  hydrogen;  2  per  cent,  sulphur;  i  per  cent. 
nitrogen,  and  7  per  cent,  ash;  the  air  required  would  be  estimated 
as  follows: 

Carbon  contained  in  a  pound  of  the  coal  equals  0.8  Ib.  From 
Table  I,  Col.  8,  air  required  for  complete  combustion  of  i  Ib. 
of  carbon  equals  11.52  Ib.  Then  the  air  required  for  0.8  Ib. 
carbon  equals 

0.8  X  11.52  =  9.216  Ib. 

The  available  hydrogen  equals  0.05  Ib.  Air  required  per  pound 
of  hydrogen  (Table  I)  equals  34.56.  Air  required  for  0.05  Ib. 
hydrogen  equals 

0.05  X  34-56  =  1.728/6. 

Adding  these  two  quantities  together,  we  have 


1 8        FUEL  ECONOMY  AND  CO2  RECORDERS 

Air  required  for  carbon  in  coal 9 . 216  Ib. 

Air  required  for  available  hydrogen 1.728  Ib. 

Air  required  per  pound  of  coal 10 . 944  Ib. 

The  air  required  for  the  sulphur  in  the  coal  we  neglect  as  the 
amount  of  sulphur  is  small  and,  besides,  the  sulphur  may  already 
be  combined  with  some  other  element  and  hence  be  incombustible 
anyhow.  The  ash  and  nitrogen,  being  incombustible,  require  no 
air. 

Two  more  illustrations  of  how  the  weight  of  air  required  for 
a  given  weight  of  fuel  is  estimated  may  assist  to  fix  the  method 
in  mind  more  securely.  Let  us  assume  that  we  are  burning  a  fuel 
oil  in  our  plant  which  is  composed  of  the  following:  Carbon,  82 
per  cent.;  available  hydrogen,  13  per  cent.;  moisture,  5  per  cent. 
How  many  pounds  of  air  are  theoretically  required  for  the  com- 
bustion of  this  oil? 

In  every  pound  of  the  oil  there  is  0.82  Ib.  of  carbon.  Then,  as 
i  Ib.  of  carbon  requires  11.52  Ib.  of  air  for  complete  com- 
bustion (see  Table  I,  Col.  8)  0.82  Ib.  will  require 

0.82  X  11.52  =  9.45  Ib. 

Then  13  per  cent,  of  a  pound  (the  amount  of  hydrogen  contained 
in  i  Ib.  of  the  oil)  equals  0.13  Ib.  Referring  again  to  Table  I, 
Col.  8,  i  Ib.  of  hydrogen  requires  34.56  Ib.  of  air  and  hence 
0.13  Ib.  requires 

0.13  X  34-56  =  449  lb. 

Adding  the  two  quantities  of  air  required,  we  have 

Air  required  by  carbon  part  of  i  Ib.  of  oil 9 . 45  Ib. 

Air  required  by  hydrogen  part  of  i  Ib.  of  oil 4.49  Ib. 

Total  air  required  per  pound  of  oil 13 . 94  Ib. 

If  we  were  burning  a  gas  containing  70  per  cent,  carbon  and 
24  per  cent,  hydrogen,  what  would  be  the  weight  of  air  required 
per  pound  of  gas? 


PRINCIPLES  OF  COMBUSTION  19 

Air  required  by  the  carbon  in  i  Ib.  of  gas  =  0.7  X  11.52   =  8.o61b. 

Air  required  by  hydrogen  in  i  Ib.  of  gas 8 . 29  Ib. 

Total  air  required  per  pound  of  gas 16 .35  Ib. 

This  same  method  of  calculating  the  amount  of  air  required  by 
a  fuel  can  be  expressed  in  the  form  of  a  formula  thus: 

w  =  11.52  c  +  34.56  (H  -  f) 

in  which 

W  =  Weight  of  air  required  per  Ib.  of  fuel; 

C  =  Weight  of  carbon  per  Ib.  of  fuel; 
LET  —  TT )  =  Available  hydrogen  per  Ib.  of  fuel. 

\  o  / 

The  available  hydrogen  is  found  by  subtracting  f  of  the  weight 
of  oxygen  in  the  fuel  from  the  total  weight  of  hydrogen  in  the  fuel 
— just  as  the  expression  in  the  formula  indicates. 

Suppose  we  had  a  fuel  with  this  analysis:  Carbon,  78  per  cent.; 
total  hydrogen,  7  per  cent.;  sulphur,  1.5  per  cent.;  oxygen,  4  per 
cent.;  nitrogen,  1.5  per  cent.,  and  ash,  8  per  cent.  Substituting 
in  the  formula  we  have 

W  =  11.52  X  0.78  +  34.56  (0.07  -   ^) 

or 

W  =  11.52  X  0.78  +  34.56  X  0.065  =  IX-23  Ib. 

of  air  required  per  pound  of  fuel. 

For  those  who  wish  to  test  their  understanding  of  what  has 
been  set  forth  in  the  foregoing  chapter  and  who  wish  practice  in 
calculations  involving  percentages  and  decimal  fractions,  the 
following  problems  are  offered: 

Given  a  coal  with  the  following  analysis:  Carbon,  78.75  per 
cent.;  total  hydrogen,  5  per  cent.;  oxygen,  2  per  cent.;  nitrogen, 
2  per  cent.;  sulphur,  3.75  per  cent.;  ash,  8.5  per  cent.  Neglecting 
the  sulphur,  what  is  the  weight  of  air  required  for  complete 


20  FUEL  ECONOMY  AND  CO2  RECORDERS 

combustion  per  pound  of  this  coal?  What  would  be  the  weight  of 
the  products  of  combustion? 

Given  a  fuel  oil  containing:  Carbon,  84.85  per  cent.;  available 
hydrogen,  11.15  Per  cent.,  and  moisture,  4  per  cent.  What  is 
the  weight  of  air  required  per  pound  of  oil  and  what  would  be  the 
weight  of  the  products  of  combustion? 

A  feed- water  heater  is  handling  7575  Ib.  of  water  per  hour.  It 
raises  the  temperature  of  the  water  from  73  to  197.5  deg.  F.  How 
much  heat  is  being  put  into  the  water  per  hour? 

These  problems  will  be  fully  worked  out  below. 

Substituting  in  the  formula  preceding  the  questions,  the  weights  of  carbon 
and  hydrogen  per  pound  of  coal  given  in  the  problem,  we  have 

w  =  11.52  c  +  34.56  (H  -  ^ 

W  =  11.52  X  0.7875  +  34.56  (0.05  -  °'°2j 

W  =  (11.52  X  0.7875  +  (34.56  X  0.0475) 
W  =  9.07  +  1.64  =  10.71  Ib. 

air  required  per  pound  of  coal.  As  the  weight  of  the  products  of  combustion 
always  equals  the  weight  of  air  required  plus  the  weight  of  the  combustibles 
themselves,  we  have 

Wt.  of  air  required  +  Wt.  of  carbon  +  Wt.  of  available  hydrogen  =  Wt.  of 
products  of  combustion 

10.71  +  0.7875  +  0.0475  =  u-54  Ib. 

In  finding  the  weight  of  air  required  for  the  combustion  of  the  fuel  oil, 
exactly  the  same  formula  is  used  as  in  the  case  of  coal,  except  that  the  avail- 
able hydrogen,  represented  by  the  term  H  —  0,  is  given  and,  a3  a  result,  our 

o 

work  is  simplified, 

w  =  11.52  c  +  34.56  (H  -  -^ 

W  =  (11.52  X  0.8485)  +  (34.56  X  0.1115) 
W  =  9-77  +  3.85  =  13.62  Ib. 


PRINCIPLES  OF  COMBUSTION  21 

of  air  required  per  pound  of  oil.     And,  in  the  same  way  as  before,  the  weight 
of  the  products  of  combustion  are 

Wt.  of  air  required  +  Wt.  of  carbon  +  Wt.  of  available  hydrogen  =  Wt.  of 
products  of  combustion 

13.62  -f  0.8485  -f  0.1115  =  14.58/6. 

According  to  the  definition  previously  given,  a  B.t.u.,  or  unit  of  heat  meas- 
urement, is  the  amount  of  heat  required  to  raise  the  temperature  of  i  Ib.  of 
water  i  deg.  F.  In  the  third  problem  there  are  7575  Ib.  of  water  per  hour  to 
be  raised  in  temperature.  Then, 

197-5  —  73  =  124.5  deg. 
7575  X  124  5  =  943,087  B.t.u. 

are  being  put  into  the  water  per  hour. 


.      CHAPTER  II 
ANALYSIS  OF  COAL 

When  you  analyze  a  fuel  you  find  out  what  it  is  composed  of. 
In  previous  lessons  we  saw  that  the  combustible  or  burnable 
makeup  of  all  fuels  consists  of  a  few  elements:  Carbon,  hydrogen 
and  sulphur.  Besides  these  combustibles  a  fuel  contains  oxygen, 
nitrogen  and  ash. 

Now  as  the  heat  value  of  a  fuel  depends  upon  the  amount  of 
carbon,  hydrogen  and  to  a  slight  extent  sulphur  which  it  contains, 
it  may  be  important  to  know  what  the  analysis  or  makeup  of  a 
given  fuel  is  so  as  to  be  able  to  estimate  what  amount  of  heat 
ought  reasonably  to  be  expected  from  its  combustion  under  the 
boiler. 

ULTIMATE  ANALYSIS 

There  are  two  kinds  of  fuel  analysis;  they  are  called  ultimate 
analysis  and  proximate  analysis.  The  ultimate  analysis  tells  the 
amount  of  carbon,  hydrogen,  oxygen,  nitrogen,  sulphur  and  ash 
which  the  dry  fuel  contains.  In  other  words,  ultimate  analysis 
means  complete  analysis,  giving  the  proportions  of  all  the 
constituents. 

To  make  an  ultimate  analysis  requires  expert  skill,  costly 
apparatus  and  a  much  more  advanced  knowledge  of  chemistry 
than  we  need  for  our  study  here.  Ultimate  analyses  are  seldom 
attempted  by  any  but  expert  chemists  in  regular  laboratories 
suitably  fitted  for  the  purpose.  However,  reports  of  ultimate 
analyses  of  the  coal  or  oil  of  a  certain  district,  seam  or  mine  are 
often  available,  and,  consequently,  it  is  well  to  know  what  an 
ultimate  analysis  is  and  how  to  use  it  in  estimating  the  heat  value 
of  a  given  fuel. 

22 


ANALYSIS  OF  COAL  23 

PROXIMATE  ANALYSIS 

The  approximate,  or  as  it  is  usually  called,  proximate  analysis, 
gives  the  amounts  or  percentages  of  moisture,  volatile  matter, 
fixed  carbon  and  ash  contained  in  the  fuel. 

Coal  is  about  the  only  fuel  to  which  the  proximate  analysis  is 
applied,  although,  of  course,  the  proximate  analysis  of  any  solid 
fuel  can  be  made.  The  proximate  analysis  of  fuel  oil  is  practically 
useless  as  in  the  average  case  there  would  be  but  one  item,  the 
oil  being  nearly  all  volatile  matter. 

The  moisture  is,  of  course,  the  amount  of  water  which  the  coal 
has  soaked  up  and  this  is  liable  to  vary  in  a  given  coal  from  time 
to  time,  depending  on  the  way  the  coal  is  stored,  state  of  the 
weather,  etc. 

The  volatile  matter  consists  principally  of  the  hydrocarbons 
described  in  the  first  lesson  on  this  subject.  When  we  say  that  a 
thing  is  volatile,  we  mean  that  it  can  be  changed  from  the  solid, 
the  semi-solid  or  from  the  liquid  state  into  a  vapor  fairly  easily, 
and  without  having  its  nature  changed;  that  is,  without  under- 
going a  chemical  change.  Quicksilver,  or  mercury,  is  a  liquid-like 
metal  which  can  be  turned  into  a  vapor,  therefore,  mercury  is 
volatile. 

In  fuels,  the  hydrocarbons  can  be  changed  into  vapors  at  fairly 
low  temperatures  and  driven  off  without  being  burned,  hence, 
they  are  called  volatile.  These  hydrocarbons  exist  in  a  great 
variety  of  form;  that  is,  although  they  all  consist  of  nothing  but 
hydrogen  and  carbon,  the  proportion  of  each  varies  greatly, 
making  substances  of  different  characteristics.  Thus,  marsh 
gas,  or  methane,  has  the  chemical  formula  CH4;  acetylene,  CzHz', 
olefiant  gas,  C2H4;  ethane,  C2H6,  etc.  Each  combination  has  its 
own  physical  qualities.  Some,  known  as  "light"  hydrocarbons, 
have  the  quality  of  vaporizing  at  fairly  low  temperatures  while 
others,  known  as  "heavy"  hydrocarbons,  do  not  vaporize  until 
the  temperature  becomes  very  high.  For  instance,  gasoline  is  a 
very  light  hydrocarbon,  as  it  changes  into  a  vapor  at  about  200 
deg.  F.,  while  cylinder  oils  are  composed  of  heavy  hydrocarbons 
because  they  remain  liquid  at  temperatures  as  high  as  600  deg. 


24        FUEL  ECONOMY  AND  CO2  RECORDERS 

The  fixed  carbon  is  the  pure  or  uncombined  carbon  which 
remains  after  the  heating  process  has  vaporized  the  hydrocarbons; 
it  can  be  driven  off  only  by  actual  burning  and  not  by  any  process 
of  vaporizing  or  distillation. 

The  ash  is  simply  the  unburnable  solid  matter  which  fuel 
contains,  and  consists  principally  of  slate,  dirt,  etc. 

The  proximate  analysis  is  not  difficult  to  make  and  it  is  valuable 
in  comparing  one  lot  of  coal  with  another,  in  estimating  the  heat 
value  and  in  checking  up  furnace  operation. 

The  proximate  analysis  consists  simply  of  heating  an  accurately 
weighed  sample  at  a  low  temperature,  for  a  certain  length  of 
time  to  dry  out  the  moisture.  The  sample  is  then  weighed  again ; 
the  loss  in  weight  divided  by  the  original  weight  is  taken  as  the 
percentage  of  moisture.  The  second  heating  (at  a  higher  tem- 
perature this  time)  and  the  third  weighing  give  the  volatile  matter. 
And  from  the  third  heating  (at  high  temperature)  and  fourth 
weighing,  the  fixed  carbon  and  ash  are  determined.  Details  of 
the  method  will  be  given  later. 

TAKING  THE  SAMPLE 

There  are  really  two  steps  to  be  taken  in  securing  a  proximate 
analysis:  First,  selecting  the  sample;  second,  making  the  analysis 
itself.  The  reliability  of  the  results  depends  upon  the  care  taken 
with  each  step. 

In  selecting  the  sample,  the  object  is  to  secure  a  small  quantity 
of  coal  which  represents  the  average  character  of  a  very  large 
quantity.  If  the  coal  were  of  uniform  character  all  the  way 
through,  or  if  the  lot  to  be  sampled  could  be  thoroughly  mixed  or 
stirred,  it  would  be  an  easy  matter  simply  to  pick  up  a  few  lumps 
or  handfuls  at  any  convenient  point  and  use  them  as  the  sample 
to  analyze.  But  as  such  is  not  the  case  it  is  necessary  to  select 
many  small  quantities  from  all  parts  of  the  lot,  of  such  size  that 
when  all  are  put  together  the  pile  will  be  small  enough  to  thor- 
oughly turn  and  mix  after  which  a  suitable  sample  can  be  taken 
therefrom.  No  exact  rules  can  be  offered  to  suit  all  cases,  and 


ANALYSIS  OF  COAL 


the  method  of  sampling  must  be  adapted  to  the  local  conditions. 
If  the  quantity  of  coal  to  be  sampled  is  large,  care  must  be  taken 
to  avoid  making  the  sample  pile  too  large  to  work  thoroughly,  yet, 
at  the  same  time,  the  pile  must  be  composed  of  as  many  small 
samples  as  possible  in  order  that  it  will  closely  represent  the  real 
character  of  the  coal. 

One  commonly  used  method  where  coal  is  received  in  carload 
lots  is  to  make  a  corer  which  can  be  driven  down  through  the  coal 
in  several  places  in  the  car.  This  method  gives  samples  of  the 
coal  from  top  to  bottom  at  the  various  points,  and  when  thor- 
oughly mixed  these  samples  may  be  taken  as  a  fair  average  for 
the  whole  car.  The  corer  may  be  made  of  heavy  2-  or  2^-in. 
iron  pipe,  5  or  6  ft.  long,  sharpened  at  one  end  and  with  the  other 
end  capped  or  reinforced  so  that  it  can  be  driven  with  a  sledge. 
Enough  samples  should  be  taken  with  the  corer  to  make  a  large 
sample  of  50  to  100  Ib.  Any  lumps  in  this  large  sample  should 
then  be  crushed  so  that 
there  are  no  pieces  larger 
than  \  in.  diameter,  after 
which  the  sample  should 
be  thoroughly  mixed  and 
' '  quartered  down  "  until 
about  5  Ib.  remain. 

This  "quartering  down" 
is  done  by  spreading  the 
sample  out  thin  in  the  shape 
of  a  circle;  dividing  this 
circle  into  quarters,  and 
throwing  away  the  first  and 
third  quarters,  as  shown  in 
Fig.  3.  Thus,  the  quantity 
is  reduced  one-half.  The 

two  remaining  quarters  are  then  mixed  thoroughly,  spread 
out  and  again  quartered.  This  process  is  continued  until  the 
remainder  of  the  sample  is  of  the  desired  size. 

If  the  sample  is  not  to  be  analyzed  right  away  it  should  be  put 


FIG.  3. — Diagram  of  method  of  quar- 
tering sample. 


26        FUEL  ECONOMY  AND  CO2  RECORDERS 

into  a  glass  jar  or  a  tin  fitted  with  a  tight  cover  and  stored  in  a 
reasonably  cool  place  until  used. 

APPARATUS  REQUIRED  FOR  PROXIMATE  ANALYSIS 

The  following  pieces  of  apparatus  or  their  equivalent  are 
required  for  making  a  proximate  analysis: 

chemist's  balance  (sensitive  to  i  milligram) $12 .00 

set  of  weights  (50  grams  to  i  milligram) 2.25 

porcelain  crucible  with  cover  (15  c.c.  capacity) 0.15 

iron  ring  stand  or  iron  tripod 0.25 

Bunsen  burner  or  gasoline  blow  torch,  25c.  or 2 . 75 

desiccator  (sulphuric  acid)  (4  in.  in  diameter) 1.25 

Ib.  sulphuric  acid  (chemically  pure) 0.30 

i  drying  oven i .  10 

i  loo-mesh  sieve  (small  size) i  .40 

1  mortar  and  pestle  (porcelain) o-  35 

2  porcelain  insulated  wire  triangles  (2-in.) 0.15 

i  pair  crucible  tongs o  •  35 

i  coffee  mill  (cast  iron) 1.15 

$23.45 

Thus,  you  see,  for  a  total  cost  of  less  than  the  price  of  a  good 
steam-engine  indicator  any  man  can  own  the  means  of  examining 
the  coal  used  in  his  plant.  And,  although  the  indicator  is  a 
splendid  instrument  for  effecting  economy,  it  is  even  more  im- 
portant to  examine  into  the  character  of  the  coal  you  purchase. 
If  the  ash  or  moisture  content  in  a  certain  lot  of  coal  is  larger  than 
normal,  you  should  know  it  and  take  steps  to  avoid  being  "  stuck  " 
in  a  similar  way  again.  If  the  character  of  the  combustible  part 
of  the  coal  undergoes  a  marked  change  you  should  know  it  in 
order  that  the  firing  methods  may,  if  necessary,  be  changed  to 
suit. 

It  certainly  is  to  the  best  interests  (in  every  sense  of  the  word) 
of  every  engineer  operating  a  coal-burning  plant,  to  analyze,  if 
not  a  sample  from  every  shipment  of  coal  received,  at  least  fre- 
quently enough  to  know  with  fair  certainty  whether  the  character 


ANALYSIS  OF  COAL 


27 


I 

cj 


1 

I 

I 

cj 

f 


28  FUEL  ECONOMY  AND  CO2  RECORDERS 

of  the  coal  changes,  and  to  keep  a  record  of  all  analyses  together 
with  the  price  of  the  coal  from  year  to  year  for  the  purpose  of 
future  reference. 

Now,  the  cost  shown  by  my  list  may  be  reduced  somewhat  by 
substituting  home-made  apparatus  and  this  point  will  be  taken  up 
as  we  discuss  each  individual  piece. 

THE  BALANCE 

The  most  important  piece  of  apparatus  is  the  balance  and  the 
price  given  in  the  list  is  that  of  about  the  cheapest  that  can  be 
used.  More  sensitive  balances,  capable  of  giving  close  results, 
would  cost  $25,  $50,  $75  or  $100.  But  for  the  average  power- 
plant  requirements  the  $12  balance  is  satisfactory  when  used 
carefully.  An  actual  picture  of  such  a  balance  is  seen  in  the 
assembly  view,  Fig.  4,  and  a  sketch  is  given  in  Fig.  5. 

The  box  rests  on  three  legs,  a  stationary  one  at  the  rear  and  the 
two  adjustable  ones  A  at  the  front  of  the  sides,  by  means  of  which 
the  balance  is  leveled.  The  leveling  in  the  present  case  must  be 
done  by  placing  a  small  spirit  level  on  the  top  of  the  box,  first 
extending  left  and  right,  then  front  and  back,  and  adjusting  the 
thumb-screws  to  suit.  Some  balances  are  fitted  with  a  small 
plumb-bob  for  leveling,  in  which  case  the  spirit  level  is  unnecessary. 

The  balance  beam,  fitted  with  a  small  knife-edge  shaft  of  hard 
steel  at  its  middle,  rests  in  the  saddle  B,  at  the  top  of  the  upright, 
which  has  V-shaped  hard-steel  bearings.  A  hard-steel  knife-edge 
shaft  at  each  end  of  the  beam  carries  a  stirrup  with  hard-steel 
V-shaped  bearings  from  which  the  scales  are  hung.  The  scale 
pans  C  are  removable.  The  saddle  B  is  raised  and  lowered  by 
means  of  the  thumb-screw  C;  in  the  lowered  position  the  scales 
rest  on  the  box,  as  shown;  in  the  raised,  they  clear  the  box  by 
about  f  in.  and  the  beam  is  thus  free  to  swing  and  indicate  whether 
the  contents  of  the  pans  are  equal  in  weight  or  not.  The  object 
of  this  arrangement  is  to  make  it  more  easy  to  load  and  unload  the 
pans.  The  balance  is  so  sensitive  that  if  you  attempted  to  lift 
one  pan  off  or  take  out  or  put  in  a  weight  much  greater  than  I 


ANALYSIS  OF  COAL  29 

gram,  the  other  pan,  unless  first  supported  or  steadied,  would 
bang  down  on  the  box  and  perhaps  upset  whatever  it  contained 
or  even  dislocate  its  stirrup  on  the  beam  above.  Thus,  before 
greatly  disturbing  the  equilibrium  it  is  convenient  to  lower  the 
pans  so  that  they  rest  on  the  box.  Of  course,  when  weighing, 
after  an  approximate  balance  has  been  established,  the  addition 
to  or  removal  from  the  weight  pan  of  a  weight  of  200  milligrams  or 
less  does  not  make  the  balance  swing  violently  and  the  pans  need 
not  be  lowered. 

Before  weighing,  the  balance  should  be  tested  by  putting  the 
empty  pans  in  the  scales,  raising  the  beam  and  noticing  whether 
the  pointer  D  either  remains  on  the  center  line  of  the  scale  E  or 
swings  an  equal  number  of  divisions  to  each  side  of  the  center 
line.  If  slight  adjustment  is  necessary  this  can  be  made  by 
turning  the  adjusting  screw  F  one  way  or  the  other  until  the  bal- 
ance is  correct.  Best  results  are  accomplished  when  the  balance 
is  placed  where  it  is  free  from  even  the  slightest  air  currents  and 
uneven  variations  in  temperature.  The  more  expensive  balances 
are  housed  in  glass  cases  which  have  fronts  that  slide  up  and  down, 
the  cases  being  closed  when  the  final  balancing  is  being  tried. 
The  ingenious  man  who  wishes  to  get  the  best  results  with  his 
$12  balance  may  build  a  glass  case  for  it,  constructing  the  case, 
of  course,  so  that  the  thumb-screw  C,  for  raising  and  lowering  the 
scales,  projects  through  the  front  and  can  be  manipulated  when 
the  front  is  closed. 

The  weights  are  furnished  in  a  special  box  which  has  compart- 
ments for  each  size  and  they  should  always  be  kept  in  the  box. 
As  soon  as  a  weight  is  removed  from  the  balance  it  should  be 
placed  directly  in  its  compartment  and  not  laid  upon  the  table 
or  anything  else  when  it  is  in  danger  of  becoming  lost,  dirty  or 
damaged.  A  pair  of  forceps  for  handling  the  weights  is  furnished 
with  every  set  and  should  always  be  used  in  preference  to  the  bare 
fingers  as  moisture  from  the  latter  is  liable  to  cause  tarnishing  or 
the  accumulation  of  dirt,  or  other  foreign  matter. 

The  weights  are  based  on  the  French  or  metric  .standards; 
the  units  used  being  grams  and  milligrams.  The  reason  for  using 


30        FUEL  ECONOMY  AND  CO2  RECORDERS 

the  French  units  instead  of  the  English  pounds,  ounces,  etc.,  is 
that  as  the  French  units  are  based  on  the  decimal  system  they 
make  calculation  more  simple.  A  gram  equals  about  0.035  °f 
an  ounce.  One  milligram  equals  TTTTHT  of  a  gram,  and,  hence 
to  reduce  grams  to  milligrams  or  vice  versa  it  is  simply  a  matter  of 
adding  the  right  number  of  ciphers  or  locating  the  decimal  point. 
To  illustrate,  526  milligrams  equal  0.526  gram;  62  grams  equal 
62,000  milligrams;  13.27  grams  equal  13,270  milligrams,  etc. 

One  set  of  weights  consists  of  one  5o-gram,  two  20-gram,  one 
lo-gram,  one  5-gram,  two  2-gram,  one  i-gram,  one  5oo-milligram, 
two  2oo-milligram,  one  ioo-milligram,  one  5o-milligram,  two 
2o-milligram,  one  lo-milligram,  one  5-milligram,  two  2-milligram 
and  one  i-milligram  weights,  so  that  their  range  is  from  i  milli- 
gram (o.ooi  of  a  gram)  up  to  iii.n  grams  advancing  by 
milligrams. 

CRUCIBLE 

The  crucible  is  the  little  vessel  in  which  the  sample  of  coal  is 
heated.  One  made  of  porcelain  will  answer  all  our  purposes.  In 
ordering,  specify  the  i5-c.c.  size  with  lid.  Its  cost  is  so  small 
that  while  a  fair  substitute  could  be  devised  it  is  not  worth  while 
doing  so  as  the  extra  care  required  in  handling  would  more  than 
offset  the  saving  effected. 

The  ringstand,  shown  in  Fig.  6,  can  easily  be  made  from 
|-in.  iron  pipe  and  fittings,  and,  being  adjustable,  it  is  more 
convenient  to  use  than  the  tripod  shown  in  Fig.  4. 

If  a  good  supply  of  gas  is  available  (as  in  almost  any  city)  a 
bunsen  burner  is  the  most  convenient  form  of  heater  to  use.  If 
not,  a  gasoline  blow  torch,  such  as  shown  in  Fig.  4,  will  be  needed; 
or  an  ordinary  plumber's  or  electrician's  torch  will  do  nicely. 
The  latter,  however,  usually  gives  a  horizontal  flame  and  will  have 
to  be  tilted  a  little  in  order  to  make  the  flame  strike  the  oven  or 
crucible  to  best  effect. 

A  home-made  Bunsen  burner  as  per  Fig.  7  will  give  just  as 
satisfactory  results  as  a  purchased  burner.  To  regulate  the  air 


ANALYSIS  OF  COAL 


32  FUEL  ECONOMY  AND  CO2  RECORDERS 

supply  a  loose  sleeve  is  placed  above  the  union  on  the  f-in. 
nipple  and  is  provided  with  four  holes  to  match  the  holes  in  the 
nipple. 

DESICCATOR 

When  the  moisture  has  all  been  driven  off  from  the  sample  of 
coal  by  the  first  heating  and  the  sample  is  dry  and  still  hot  it  would 
rapidly  absorb  moisture  from  the  air  if  left  exposed  to  it  in  that 
condition.  And  the  same  thing  would  happen  after  each  subse- 
quent heating  if  the  sample  were  left  exposed  to  the  ordinary  air. 

Hence,  the  sample  is  transferred  direct  from  the  oven  or  from 
the  tripod  to  the  desiccator  or  drier  to  cool  off  before  being 
weighed.  The  commonest  form  of  desiccator  is  that  shown  in 
Fig.  4.  It  consists  simply  of  a  glass  jar  and  lid;  the  joint  between 
jar  and  lid  being  ground  to  an  air-tight  fit.  The  lower  part  or 
well  of  the  desiccator  is  about  quarter  or  half  filled  with  pure 
sulphuric  acid.  The  upper  part  contains  a  glass  or  porcelain  tray 
upon  which  to  set  the  crucible  containing  the  sample  of  coal. 

The  principle  of  the  desiccator  is  this:  Sulphuric  acid  has  a 
strong  affinity  for  water  or  moisture.  Hence,  with  an  air-tight 
lid,  what  little  moisture  there  is  in  the  air  entrapped  in  the  desic- 
cator is  soon  absorbed  by  the  acid  and  the  hot  sample  of  coal  does 
not  get  a  chance  to  absorb  any  moisture  and  thus  cause  an  error 
in  the  analysis. 

One  pound  of  chemically  pure  sulphuric  acid  (enough  for  use  in 
the  desiccator  for  a  long  time)  can  be  purchased  for  3oc.;  this 
includes  the  glass-stoppered  bottle  to  contain  it.  How  long 
the  acid  in  the  desiccator  will  remain  effective  depends  on  the 
manner  in  which  it  is  used.  If  means  are  available  for  accurately 
weighing  the  acid  or  the  desiccator  before  and  after  the  acid  has 
been  put  in,  the  acid  may  be  renewed  when  the  gain  in  weight  is 
equal  to  25  per  cent,  of  the  original  weight  of  the  acid.  To 
illustrate,  suppose  J  Ib.  (or  about  113  grams)  of  the  dry  acid  were 
put  into  the  desiccator  and  after  six  months  or  a  year,  the  weight 
was  found  to  be  5  oz.  (a  gain  of  25  per  cent.)  it  would  then  be 


ANALYSIS  OF  COAL  33 

advisable  to  refill  the  desiccator  with  fresh  acid.  If  it  is  not 
convenient  to  check  up  the  condition  of  the  acid  by  weighing,  it  is 
safest  to  renew  it  about  once  a  year. 

Great  caution  must  be  used  in  handling  sulphuric  acid  as  it  will 
attack  or  "eat  away"  the  clothing,  also  iron,  copper  and  many 
other  metals.  And,  if  it  comes  in  contact  with  flesh  it  may 
cause  a  bad  burn.  Keep  the  bottle  where  it  is  not  in  danger  of 
being  broken  and  be  sure  that  none  of  the  acid  is  allowed  to  spill 
out  of  the  desiccator.  Also,  never  allow  any  water  to  come  in 
contact  with  the  acid  as  much  heat  is  generated  thereby  and  the 
acid  might  spatter  on  the  face  and  hands.  Always  keep  the  lid 
on  the  desiccator  to  prevent  the  acid  from  absorbing  moisture 
from  the  air  and  thus  becoming  weakened  too  soon. 

DRYING  OVEN 

The  drying  oven  is  used  for  the  first  heating  of  the  sample  to 
determine  the  moisture  content. 

If  you  were  to  purchase  a  standard  oven  it  would  cost  at  least 
$5.  The  oven  shown  in  Fig.  4  can  be  manufactured  for  $1.10  or 
even  less.  Secure  a  i-qt.  tin  pail  (about  4  in.  in  diameter  by 
about  4J  in.  high)  cost  ice.  Punch  a  hole,  about  ii  in.  in  diame- 
ter, in  the  center  of  the  lid.  Next,  secure  a  good  sound  cork  to 
fit  the  hole  and  bore  a  hole  in  the  cork  so  that  .the  thermometer 
will  fit  in  it  snugly,  as  shown. 

See  that  the  lid  of  the  pail  fits  loosely  so  that  it  can  be  removed 
without  the  necessity  of  holding  the  pail,  as  the  latter  will  be  hot 
and  awkward  to  handle  most  of  the  time  and  the  sample  might  be 
spilled  if  force  is  used.  If  necessary,  cut  off  or  bend  in  the  flange 
on  the  lid.  Punch  a  hole  about  i  in.  in  diameter  in  the  bottom 
of  the  pail  and  one  or  two  small  ones  in  the  lid  to  provide  for  a 
small  circulation  of  air. 

Purchase  a  chemical  thermometer  having  a  range  from  zero  to 
200  deg.  C.,  cost  $i.  Insert  this  in  the  cork,  as  shown  in  Fig.  4, 
so  that  the  bulb  projects  into  the  pail  about  if  in. 

Bend  down  the  ends  of  a  porcelain-insulated  wire  triangle  so  as 


34        FUEL  ECONOMY  AND  CO2  RECORDERS 

to  form  a  little  stand  for  the  crucible,  as  shown  in  Fig.  8.  Put 
this  stand  in  the  pail  and  place  the  pail  on  the  ringstand  or  tripod 
over  the  burner  and  our  home-made  oven  is  ready  for  "business." 
The  next  item  on  our  list,  the  loo-mesh  sieve,  is  desirable  but 
not  absolutely  essential.  It  is  used  for  sifting  the  sample  before 
the  analysis.  If  economy  in  first  cost  is  imperative,  the  sample 
may  be  prepared  without  sifting,  but  extreme  care  should  be  used 
to  crush  the  sample  uniformly  and  as  fine  as  possible. 


-No.  12  Iron  Wire 

FIG.  8. — Home-made  triangles. 

The  mortar  and  pestle,  for  crushing  the  sample,  may  also  be 
dispensed  with  if  desired;  but  the  price  is  so  small  and  they  are  so 
convenient  that  this  is  not  recommended.  If  the  sample  is 
crushed  with  a  hammer  in  an  iron  pot,  on  a  sheet  of  iron,  slab  of 
stone  or  other  hard  surface,  care  must  be  taken  that  particles  of 
incombustible  foreign  matter  do  not  get  mixed  with  the  coal,  thus 
causing  an  error  in  the  analysis. 

The  next  item  on  the  list,  the  porcelain-insulated  wire  triangles, 
are  used,  one  for  supporting  the  crucible  on  the  tripod  or  ringstand 


ANALYSIS  OF  COAL  35 

over  the  flame,  the  other,  bent  as  just  described,  for  supporting 
the  crucible  in  the  drying  oven.  Satisfactory  home-made  tri- 
angles may  be  made  as  shown  in  Fig.  8. 

The  crucible  tongs,  shown  in  Fig.  4,  are  used  for  handling  the 
crucible  and  lid  throughout  the  analysis.  A  pair  of  home-made 
tongs  could  be  devised,  but  it  is  doubtful  if  the  effort  is  worth 
while  as  they  probably  would  not  be  as  "handy"  or  as  smooth 
working  as  a  purchased  pair. 

The  last  item  on  the  list,  the  coffee  mill,  is  employed  to  coarsely 
grind  the  sample  before  it  receives  the  final  mixing  and  crushing. 
If  an  old  coffee  mill  is  available,  so  much  the  better,  as  it  will 
answer  just  as  well  as  a  new  one  and  the  cost  of  the  new  one  will 
be  saved.  It  should  be  strong  enough,  however,  to  stand  the  serv- 
ice. One  made  of  cast  iron  would  be  suitable. 

MAKING  THE  ANALYSIS 

You  have  now  been  introduced  to  all  the  apparatus  needed  in 
making  a  proximate  analysis  and  all  that  remains  to  be  acquired 
is  a  little  practice  in  handling  the  equipment  and  running  the 
actual  analysis.  Run  five  or  six  analyses  just  for  the  practice. 

From  the  outset,  remember  that  the  more  careful  and  pains- 
taking you  are  with  the  work,  the  more  accurate  and  reliable  will 
be  the  results.  The  sample  dealt  with,  i  gram,  and  the  differ- 
ences to  be  determined  in  the  weight  of  that  sample  after  each 
step,  are  so  small  that  it  requires  but  a  slight  inaccuracy  to  throw 
out  the  entire  work. 

Get  into  the  habit  of  following  exactly  the  same  process  with 
each  analysis.  Do  not  use  one  method  one  day  and  then  vary  it, 
even  slightly,  the  next.  Decide  by  experiment  in  the  beginning 
the  best  method  for  you  to  follow  and  stick  as  closely  to  that 
method  as  possible  with  all  your  analyses.  The  object  of  this 
advice  is  to  insure  uniformity  in  results.  If  you  use  one  method 
one  day  and  a  slightly  different  method  the  next,  the  results  are 
not  likely  to  be  uniform.  And  what  you  want  is  a  fair  comparison, 
one  day  with  another. 


FUEL  ECONOMY  AND  CO,  RECORDERS 


A  good  method  to  follow  is  this:  Assume  that  a  5-lb.  sample  of 
the  coal  to  be  tested  has  been  collected  as  described.  Rule  off  a 
form  on  which  to  record  the  analysis.  The  one  shown,  already 
filled  out,  in  Fig.  9  is  convenient  but  may  need  slight  modifications 
to  suit  special  needs.  If  you  expect  to  analyze  coal  regularly,  it 
will  pay  to  have  the  form  printed  or  mimeographed. 

First,  see  that  the  crucible  is  thoroughly  clean  and  dry.  Then 
weigh  it,  together  with  its  cover,  as  accurately  as  possible,  remem- 


PROXIMATE  ANALYSIS  OF  COAL 

piant  ^.?r^tyfc-..'tt^r.  

Car  No»    fc  *'  &  TSf^M^K/^^-     Total  Tons  it 

i  Shipment.  .<$?  

Analyred>»r-/^^ 

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Date.Recflived^?*r*^/'/.Date  Sample 
Ant 

Takenji?*$.?/.Datt 
Jyted  by  fexfi*** 

Grams 

Analysis 
of  Coal  as 
Received 

Analysis 
of  Dry 
Coal 

Wt.  of  crucible  and  lid 

<*/.£«. 

P           »n       p 

Wt.  leas  moisture  

2/.y<SS 

Per  cent,  moisture 

27 

Wt.  less  volatile  matter.  . 

*/.  /6jT 

Per  cent.  vol.  matter 

A/.<T 

30.  J-^ 

Wt.  less  fixed  carbon  

AP.  6  3J 

Per.cent.  fixed  carbon 

S3.0 

Jf.y-z 

Wt.    of    empty    crucible 
with  lid  

fy.  S£2* 

Per  cent,  ash  

//.<T 

/*** 

Heat  value  of  dry  coal 
(by  calorimeter)  B.t.u.  per  Ib 
Heat  value  of  combust- 
ible .(estimated)  tiffi&.'B.i.vi.  per  Ib 
Heat  value  of  dry  cbal 
(estimated).  &?£%,..  B.t.u.  per  Ib 
Heat  value  of  coal  as  received 
(estimated)  M*frA*.  .  .B.t.u.  per  Ib 

.     Cost  of  Coal,  %....  "^'.7°.  ....  per  ton 
No.  B.t.u.  purchased       '  r+fg? 
for  1  cent              .     <^Jr./T.  

. 

FIG.  9. — Proximate  analysis  report  form. 

bering  to  test  the  balance  first.  Weigh  the  crucible  and  cover 
before  every  analysis,  to  be  sure  that  the  weight  is  accurate,  for 
if  a  slight  chip  should  break  off  from  either,  the  results  would  be 
wrong  unless  the  new  weight  of  the  crucible  were  used.  Enter 
the  weight  in  the  proper  space  on  the  report  sheet.  Then,  fill 
out  the  first  space  by  adding  i  gram  to  the  weight  of  crucible 
and  lid. 


ANALYSIS  OF  COAL  37 

When  weighing  it  is  not  necessary  to  wait  for  the  balance  to 
come  to  rest  each  time;  simply  notice  whether  the  pointer  swings 
uniformly  a  given  number  of  divisions  each  side  of  the  center  line 
on  the  scale.  But  be  sure  that  the  swing  is  exactly  uniform. 
Leave  the  crucible  in  the  scale  pan  ready  to  receive  the  sample. 

Spread  out  the  5-lb.  sample  on  a  clean  surface  (such  as  a  piece 
of  newspaper)  mix  thoroughly  and  quarter  down  to  about  i 
Ib.  Put  this  quantity  through  the  coffee  mill  once  or  twice, 
grinding  as  fine  as  possible  with  the  mill.  Again  mix  and  spread 
out  thin  on  a  clean  surface.  Then,  with  a  knife  blade,  select 
small  quantities  from  a  half  dozen  places  in  the  mass  and  put  them 
in  the  mortar,  thus  obtaining  about  i  oz.  Crush  thoroughly 
with  the  pestle.  Sift  this  finely  crushed  sample  through  the  100- 
mesh  sieve  into  the  tray  that  comes  with  the  latter.  If  any  of  the 
sample  will  not  pass  through,  put  it  back  into  the  mortar  and  crush 
until  practically  all  passes  through. 

If  you  are  working  without  a  sieve  be  sure  that  the  sample  is 
crushed  fine  enough.  It  should  look  like  a  very  fine  dust — so  fine 
and  uniform  that  no  individual  particles  are  distinguishable. 

Now,  add  i  gram  to  the  weights  in  the  balance  and  put 
enough  of  the  powdered  sample  into  the  crucible  to  again  restore 
equilibrium. 

Put  the  crucible  (without  cover)  into  the  oven  and  heat  to  no 
deg.  C.  for  i  hour.  Keep  heat  as  uniform  as  possible.  Now, 
quickly  transfer  the  crucible  to  the  desiccator  and  allow  it  to  cool 
off.  This  will  take  about  10  minutes.  When  cool,  weigh  crucible 
(with  lid  on)  and  enter  weight  in  the  second  space  on  the  report 
sheet.  Subtract  this  weight  from  the  one  above,  move  the  decimal 
point  two  places  to  the  right  and  enter  result  as  percentage  of 
moisture  in  the  proper  space. 

Next,  place  the  crucible,  with  lid  on  and  in  an  upright  position, 
on  the  triangle  and  ringstand  over  the  burner,  as  shown  at  the 
left  in  Fig.  4.  Turn  the  flame  up  strong  and  heat  the  crucible 
for  full  7  minutes.  The  flame  should  be  long  enough  and  placed 
close  enough  to  the  crucible  to  completely  envelop  it  and  shoot 
above  for  a  distance  of  an  inch  or  more. 


38        FUEL  ECONOMY  AND  CO,  RECORDERS 

At  the  end  of  the  7  minutes  remove  the  flame  and  transfer  the 
crucible  and  lid  to  the  desiccator  to  cool.  Inspect  the  sides  of  the 
crucible  to  make  sure  that  the  porcelain  insulators  on  the  triangles 
have  not  softened  under  the  heat  and  left  small  particles  sticking 
to  the  former.  If  this  occurs  the  analysis  will  have  to  be  done 
over,  as  the  weighing  would  be  inaccurate.  If  this  occurs  fre- 
quently, a  "Nichrome"  wire  triangle  will  have  to  be  used  instead 
of  the  porcelain  insulated  one.  The  cost  of  one  of  this  kind  is 
about  3$c.,  but  it  is  durable  and  will  not  stick. 

In  heating  to  drive  off  the  volatile  matter  a  black  smudge  of 
carbon  will  probably  be  made  on  the  outside  of  the  crucible. 
Most  people  burn  this  off  before  transferring  to  the  desiccator  by 
playing  the  flame  on  the  sides.  I  am  not  going  to  advise  you  to 
do  this  because,  unless  carefully  done,  it  leads  to  the  breakage  of 
crucible  or  lid,  thus  spoiling  an  analysis.  Besides,  the  error  caused 
is  so  very  slight  that  it  is  hardly  worth  the  trouble  taken  to 
eliminate  it,  and,  if  the  same  practice  is  followed  each  time,  the 
importance  of  the  error  is  still  more  reduced.  However,  before 
another  analysis  is  made  in  the  crucible  both  it  and  the  lid  should 
be  cleaned  by  carefully  burning  off  this  carbon  deposit. 

When  the  crucible  is  cool,  weigh  and  enter  the  weight  as  before. 
The  loss  in  weight  this  time  represents  the  percentage  of  volatile 
matter  contained  in  the  coal. 

Next,  place  the  crucible,  without  cover,  on  the  stand  again, 
only  this  time  tilt  it  as  far  on  its  side  as  you  can  without  danger 
of  any  of  the  contents  being  spilled  or  blown  out.  Turn  the  flame 
on  strong,  as  before,  and  heat  thus  for  at  least  2  hours.  See 
that  the  flame  concentrates  under  that  part  where  the  sample  lies. 

At  the  end  of  the  heating,  cool  in  the  desiccator  and  weigh 
again  with  the  lid.  The  loss  in  weight  this  time  represents  the 
percentage  of  fixed  carbon.  And,  the  difference  between  this 
last  weight  and  the  weight  of  the  empty  crucible  with  lid  repre- 
sents the  percentage  of  ash  in  the  coal. 

The  analysis  is  now  finished  and  all  that  remains  is  to  stow  the 
apparatus  safely  away  until  next  needed  and  to  calculate  the 
analysis  of  the  dry  coal. 


ANALYSIS  OF  COAL  39 

The  analysis  which  we  have  just  completed  is  that  of  the  coal 
"as  received."  Strictly  speaking,  it  is  not  the  true  analysis  of 
the  coal  as  received  because  some  of  the  moisture  dried  out  while 
the  sample  was  being  prepared  for  testing.  But,  as  long  as  about 
the  same  length  of  time  is  taken  up  in  preparing  the  sample  in 
each  case  and  as  long  as  the  process  of  treatment  is  the  same,  the 
error  remains  about  the  same  and,  so,  we  may  call  it  the  "as 
received"  analysis  and  do  no  particular  harm. 

With  some  grades  of  coal  which  have  a  great  capacity  for 
absorbing  moisture  it  is  necessary  to  air  dry  the  sample  before  it 
can  be  passed  through  the  sieve.  In  such  cases  if  extreme  ac- 
curacy is  important,  a  preliminary  air-drying  test  must  be  made 
and  the  moisture  thus  eliminated  must  be  included  in  the  calcu- 
lations. But  as  this  complicates  matters  somewhat,  I  do  not 
recommend  that  it  be  attempted  in  ordinary  work.  If  the  coal  will 
not  sift  through  the  sieve  readily  when  first  crushed,  it  may  be 
allowed  to  stand  exposed  to  the  air  for  one-half  to  one  hour.  A 
better  method  to  employ,  because  it  insures  more  uniform  analyses, 
is  to  coarse  grind  a  sample  of  a  pound  or  two  in  the  coffee  mill,  spread 
it  out  in  a  thin  layer  and  leave  it  exposed  to  the  air  at  70  to  80  deg. 
F.  for  24  hours.  If  this  method  is  adopted  regularly,  the  term 
"air  dried"  should  be  substituted  for  "as  received"  throughout 
the  report  form  in  Fig.  9. 

To  figure  the  analysis  of  the  dry  coal  from  the  analysis  of  the 
"as  received"  sample,  simply  divide  the  percentage  of  volatile 
matter,  fixed  carbon  and  ash  (each  in  turn)  by  the  sum  of  all 
three.  Thus,  taking  the  analysis  given  in  Fig.  9,  the  sum  of  the 
percentages  of  volatile  matter,  fixed  carbon,  and  ash  is, 

27-8  +  53  +  ii-S  =  92-3 
This  sum  divided  into  the  percentage  of  volatile  matter  gives 

27.8 

-  =  30.12 
92-3 

as  the  percentage  of  volatile  matter  in  the  dry  coal. 

The  reason  is  simple.  Let  us  assume  100  Ib.  of  coal  of  the 
analysis  given.  As  the  analysis  shows  7.7  per  cent,  moisture, 


40  FUEL  ECONOMY  AND  CO2  RECORDERS 

7.7  lb.  is  water,  leaving  only  92.3  Ib.  when  the  coal  is  thoroughly 
dry.  The  analysis  also  shows  27.8  lb.  volatile  matter  in  every 
100  lb.  of  the  coal  as  received.  Then,  what  fraction  of  the  dry 
coal  is  the  volatile  matter? 

27.8 

=  0.3012  or  30.12  per  cent. 

In  a  like  manner,  the  percentages  of  the  other  two  constituents, 
fixed  carbon  and  ash,  are  figured. 


ESTIMATING  HEAT  VALUE  OF  FUEL 

The  heat  value  of  a  fuel  is  estimated  either  by  actually  burning 
a  small  sample  and  measuring  the  heat  given  off  or  by  calculation 
based  on  either  the  ultimate  or  the  proximate  analysis.  The 
first  is  the  more  accurate  method,  but  as  the  cost  of  the  required 
apparatus  is  rather  high,  and  as  it  is  not  important  for  everyday 
work  to  know  the  exact  heat  value  of  every  lot  of  coal  received, 
we  will  pay  most  attention  to  the  second  method  and  pass  over 
the  first  after  giving  a  brief  description  in  order  that  you  may  be 
familiar  with  it  in  a  general  way. 

COAL  CALORIMETER 

The  sample  burned  is  as  carefully  selected  and  prepared  as  the 
sample  used  for  the  proximate  analysis,  and  its  weight  is  usually 
the  same,  i  gram.  It  is  burned  in  a  device  called  a  calorimeter — 
a  name  derived  from  the  words  caloric,  meaning  heat,  and  meter, 
meaning  measurer. 

Fig.  10  illustrates  a  simple  form  of  the  commonest  type  of  coal 
calorimeter.  The  bomb  or  crucible  C  of  iron  or  steel  and  lined 
with  some  material  which  is  not  affected  by  the  products  of 
combustion,  contains  the  sample  of  coal  to  be  tested,  and  is 
suspended  in  the  water  chamber  B  as  shown.  This  water 
chamber  is  surrounded  by  the  casing  A  to  reduce  error  due  to 
radiation.  The  stem  F  is  hollow  and  closed  off  at  the  upper  end 


ANALYSIS  OF  COAL  41 

by  a  valve.  The  wooden  lid  H  is  tight  fitting.  To  load  the  bomb 
C  it  is  taken  out  and  unscrewed  from  the  cap  G.  The  sample  of 
coal,  thoroughly  mixed  with  the  proper  amount  of  some  chemical 
which  gives  up  oxygen  when  heated  (usually  sodium  peroxide)  is 
put  into  the  bomb  and  the  latter  is  again  screwed  into  place. 


FIG.  10. — Simple  form  of  coal  calorimeter. 


A  quantity  of  water,  which  has  been  exactly  measured,  is  then 
put  into  B,  and  when  the  lid  H  is  again  fixed  in  place,  the  calor- 
imeter is  ready  for  the  test.  The  water  is  stirred  for  a  few  minutes 
with  the  paddle  D  until  the  thermometer  E  shows  that  the  tem- 
perature has  ceased  changing.  Then  the  valve  at  the  top  of  the 


42  FUEL  ECONOMY  AND  CO2  RECORDERS 

stem  F  is  opened,  a  small  piece  of  red-hot  nickel  wire  is  dropped  in 
and  the  valve  quickly  closed  again. 

Rapid  and  complete  combustion  takes  place  due  to  the  libera- 
tion of  the  oxygen  from  the  chemical  mixed  with  the  coal.  The 
heat-laden  products  of  combustion  are  all  trapped  in  the  bomb 
and  hence  must  give  up  their  heat  to  the  surrounding  water,  which 
is  again  stirred  for  several  minutes  to  hasten  the  transfer  and  to 
maintain  uniformity.  The  rise  in  the  temperature  of  the  water 
is  carefully  noted,  the  thermometer  being  graduated  to  read  in 
small  fractions  of  a  degree. 

Knowing  the  weight  of  the  water  and  the  rise  in  temperature, 
the  number  of  heat  units  generated  by  the  sample  can  easily  be 
calculated  by  multiplying  these  two  factors  together,  and  the  heat 
value  of  a  pound  of  fuel  can  then  be  found  by  multiplying  by  a 
constant,  which  takes  into  account  the  ratio  of  weights  and  other 
factors  involved. 

HEAT  VALUE  BY  CALCULATION 

As  has  been  pointed  out,  the  combustion  of  a  given  element 
always  results  in  the  generation  of  a  fixed  amount  of  heat.  Thus, 
when  a  pound  of  pure  carbon  burns  completely  (forming  COz) 
14,600  B.t.u.  is  produced.  When  2  Ib.  is  burned,  29,200  B.t.u.  is 
generated,  and  so  on.  Consequently,  the  heat  value  of  carbon  is 
said  to  be  14,600  B.t.u.  —  which  means  14,600  B.t.u.  per  Ib.,  as  the 
pound  is  the  unit  of  weight  almost  universally  used  in  this 
country. 

When  a  pound  of  pure  carbon  burns  incompletely  (forming 
CO),  only  4450  B.t.u.  is  produced.  But  if,  in  turn,  the  resulting 
2\  Ib.  of  CO.,  which  is  a  combustible  gas,  is  burned,  10,150 
additional  B.t.u.  is  liberated,  making  the  total  heat  produced 
equal  to  14,600  B.t.u.,  just  the  same  as  though  the  pound  of 
carbon  had  burned  completely  (to  C02)  in  the  first  place.  Hence, 
the  heat  value  of  CO  is 


-  =  43  50  B.t.u.  per  Ib. 


ANALYSIS  OF  COAL  43 

The  heat  value  of  pure  hydrogen  is  62,000  B.t.u.  per  Ib. 

These  heat  values  for  carbon  and  hydrogen  were  established  by 
experiment  and  hence  probably  are  not  absolutely  exact.  In 
fact,  some  authorities  give  values  for  carbon  as  low  as  14,220, 
and  as  high  as  14,647,  and  for  hydrogen  as  low  as  61,816  and  as 
high  as  62,032,  but  as  the  ones  given  (14,600  and  62,000)  are  the 
most  widely  accepted  and  used,  it  is  best  to  accept  them  for  use 
in  our  work. 

The  heat  value  of  sulphur,  the  only  other  heat-producing  ele- 
ment in  the  common  fuels,  is  4050  B.t.u.  per  Ib.  While  this  fact 
is  interesting,  it  is  not  important  in  practical  work,  because  in 
addition  to  the  heat  value  of  the  sulphur  itself  being  low,  the 
percentage  of  sulphur  in  the  average  fuel  is  also  low;  besides,  the 
sulphur  may  not  be  pure  and  hence  may  have  no  heat  value 
whatever.  Thus  the  amount  of  heat  due  to  the  sulphur  is  very 
small  compared  with  that  given  up  by  the  two  main  elements, 
carbon  and  hydrogen. 

To  estimate  the  heat  value  of  a  pound  of  fuel  containing  both 
carbon  and  hydrogen,  simply  multiply  the  percentage  of  total 
carbon  in  the  fuel  (expressed  as  a  decimal)  by  14,600,  the  percent- 
age of  available  hydrogen  (also  expressed  as  a  decimal)  by  62,000 
and  add  the  results  together. 

To  illustrate,  assume  we  wish  to  estimate  the  heat  value  of  a 
coal  with  this  analysis:  Carbon,  68.12  per  cent. ;  hydrogen,  4.98 
per  cent.;  oxygen,  7.42  per  cent.;  nitrogen,  1.98  per  cent. ; sulphur, 
4.54  per  cent.;  ash,  12.96  per  cent. 

The  heat  due  to  the  carbon  is 

0.6812  X  14,600  =  9945.5  B.t.u. 

The  available  hydrogen  equals 

0.0742 
0.0498  —  — Q —  =  0.0405 

o 

I  and  this,  multiplied  by  the  heat  value  of  hydrogen, 

0.0405  X  62,000  =  2511  B.t.u., 


44        FUEL  ECONOMY  AND  CO2  RECORDERS 

the  heat  due  to  the  hydrogen  in  the  coal.     The  sum  of  these  two 
quantities  is 

9945.5  +  2511  =  12,456.5  B.tu. 
the  heat  value  of  the  coal. 

HEAT  VALUE  BY  FORMULA 
The  foregoing  method  can  be  expressed  in  a  formula  as  follows: 


C  X  14,600+   H  -  -g     62,000  =  B.t.u.  perlb. 

where 

C  =  Decimal  part  by  weight  of  carbon  in  the  fuel; 
H  =  Decimal  part  by  weight  of  hydrogen  in  the  fuel; 
O  =  Decimal  part  by  weight  of  oxygen  in  the  fuel. 

To  apply  this  formula  to  another  example,  assume  a  coal  with 
this  analysis:  Carbon,  65.23  per  cent.;  hydrogen,  4.95  per  cent.; 
oxygen,  14.85  per  cent.;  nitrogen,  1.66  per  cent.  ;  sulphur,  2.10  per 
cent.;  ash,  11.21  per  cent.  Substituting  in  the  formula,  we  have 


/  o.i485\ 

0.6523   X   14,600  +  (0.0495  --  ~~g      j   62,000 

=  n,439  £•*•«• 

The  foregoing  method  of  formula  may  be  used  for  any  other  kind 
of  fuel  or  for  oil,  wood,  gas,  etc.  In  dealing  with  gas,  however, 
care  must  be  used  that  volumes  and  weights  are  not  confused  to 
produce  error.  A  common  method  of  stating  the  heat  value  of 
a  fuel  gas  is  in  B.t.u.  per  cubic  foot  or  per  1000  cu.  ft.  In  such 
cases  the  temperature  and  pressure  of  the  gas  must  also  be  speci- 
fied because  these  influence  the  volume  greatly.  The  temperatures 
most  frequently  taken  are  32  and  60  deg.  F.,  and  the  pressure, 
14.7  lb.,  absolute. 

HEAT  VALUE  FROM  PROXIMATE  ANALYSIS 

The  proximate  analysis  of  coal  does  not  give  the  percentage  of 
hydrogen,  the  percentage  of  oxygen  nor  the  percentage  of  total 


ANALYSIS  OF  COAL  45 

carbon.  It  does  give  the  percentage  of  fixed  carbon,  but  in  addi- 
tion to  this  the  fuel  contains  some  carbon  which  forms  part  of 
the  volatile  matter  and  the  amount  or  percentage  of  this  volatile 
carbon  cannot  be  found  except  by  the  ultimate  analysis.  Hence, 
the  formula  just  given  is  of  use  only  in  those  few  cases  where  the 
ultimate  analysis  is  available,  so  that  other  methods  will  mostly 
have  to  be  used  in  our  work. 

Some  relation  exists  between  the  percentage  of  fixed  carbon 
in  the  combustible  matter  of  coal  and  the  heat  value  of  the  com- 
bustible matter.  To  illustrate,  if  the  combustible  matter  of  a 
given  coal  consists  of,  say,  60  per  cent,  fixed  carbon  and  the 
other  40  per  cent,  volatile  matter,  it  is  probable  that  the  heat 
value  of  a  pound  of  such  combustible  matter  will  be  found  to 
be  about  15,080  B.t.u.  This  does  not  apply  closely  to  all 
coals,  but  it  applies  closely  enough  to  most  coals  to  be  useful  in 
the  absence  of  a  better  or  more  accurate  method  of  estimation 
that  can  be  used  with  the  proximate  analysis. 

Fig.  ii  is  based  on  this  fact.  This  chart  was  constructed  from 
over  300  analyses,  representing  coal  found  in  27  states  and 
territories,  made  by  the  United  States  Government  and  published 
in  numerous  bulletins.  It  is  almost  exactly  correct  for  a  limited 
number  of  cases,  reasonably  near  correct  (probably  within  3 
per  cent.)  for  a  large  number  of  cases  and  quite  far  from  correct 
in  a  few  cases.  The  curve  is  most  uniformly  accurate  for  coals 
which  have  combustible  matter  containing  from  64  to  90  per  cent, 
fixed  carbon.  Where  the  fixed  carbon  runs  less  than  64  per  cent, 
the  curve  may,  in  a  few  cases,  err  as  much  as  7  per  cent. 

APPLICATION  OF  CHART 

To  estimate  the  heat  value  of  a  coal  with  a  given  proximate 
analysis,  add  together  the  percentage  of  fixed  carbon  and  the 
percentage  of  volatile  matter  in  the  coal;  divide  this  sum  into 
the  percentage  of  fixed  carbon  and  multiply  by  100.  This  gives 
the  percentage  of  fixed  carbon  in  the  combustible  matter.  Locate 
this  percentage  at  the  foot  of  the  chart,  extend  your  pencil  straight 


46 


FUEL  ECONOMY  AND  CO2  RECORDERS 


C  Is 
fl» 


o      o 
o      o 


o      o      o      o      o 

O  O  O  O  o 
•n'ttorvi  —  O0>ot> 
M?4fm<A«)*?-^V 


O  O  O  O  O 

o  o  o  o  o 

h*  ^  »o  ^  10 

•»  t"  V  V  *" 


O  O  O 

o  o  o 

M  -  O 

V  T"  ^" 


•n      *    -a 


ANALYSIS  OF  COAL  47 

up  until  you  strike  the  curve,  then  extend  it  to  the  nearest  (left 
or  right)  margin  in  a  straight  horizontal  line  and  read  off  the 
B.t.u.  per  pound  of  combustible.  Multiply  the  B.t.u.  thus 
found  by  the  sum  of  the  percentage  of  fixed  carbon  and  volatile 
matter  in  the  coal  as  shown  by  the  proximate  analysis,  and  the 
answer,  divided  by  100,  gives  the  B.t.u.  per  pound  of  coal. 

To  illustrate  with  an  actual  example,  assume  a  coal  with  this 
proximate  analysis:  Moisture,  5.12  per  cent.;  volatile  matter, 
27.25  per  cent;  fixed  carbon,  53.38  per  cent.;  ash,  14.25  per  cent. 
Adding  together  the  percentage  of  fixed  carbon  and  the  percentage 
of  volatile  matter, 

53.38  +  27.25  =  80.63. 

Dividing  this  into  the  fixed  carbon,  we  have 

53.38  -T-  80.63  =  0-662, 

which,  multiplied  by  100,  gives  66.2  per  cent,  fixed  carbon  in  the 
combustible.  Referring  to  the  base  line  of  the  chart,  find  the 
66  per  cent,  line  and  judge  a  point  0.2,  or  ^-,  of  the  distance  to  the 
next  line  beyond.  Trace  an  imaginary  vertical  line  (this  line  is 
shown  dotted  on  the  chart)  up  from  this  point  to  the  curve  and 
then  horizontally  to  the  left  margin.  It  strikes  exactly  the  15,400- 
B.t.u.  line.  Then,  15,400  B.tu.  may  be  taken  as  the  heat  value 
of  a  pound  of  combustible  matter  such  as  found  in  the  coal 
given  in  the  example. 

Now,  if  the  coal  was  all  combustible  and  had  no  moisture  nor 
ash,  the  heat  value  per  pound  of  coal  would  be  identical  with  the 
heat  value  per  pound  of  combustible.  But  only  80.63  Per  cent- 
of  the  coal  is  combustible,  and  hence  the  heat  value  of  a  pound 
of  coal  is  equal  to  only  80.63  per  cent,  of  the  heat  value  of  a  pound 
of  combustible.  Thus,  the  heat  value  of  the  coal  is 

15,400  X  80.63  -T-  100  =  12,417  B.t.u. 

EXERCISE  PROBLEMS 

What  is  the  heat  value  of  a  coal  with  the  following  ultimate 
analysis:  Carbon,  63.65  per  cent;  hydrogen,  5.26  per  cent; 


48        FUEL  ECONOMY  AND  CO,  RECORDERS 

oxygen,  10.12  per  cent;  nitrogen,  1.59  per  cent;  sulphur,  5.03 
per  cent;  ash,  14.35  Per  cent? 

Estimate  the  heat  value  of  a  coal  which  has  this  proximate 
analysis:  Moisture,  1.36  per  cent ;  volatile  matter,  35.51  per  cent.; 
fixed  carbon,  50.06  per  cent;  ash,  13.07  per  cent. 

Following  are  the  solutions  of  the  problems  in  the  above  para- 
graph. Applying  the  formula  given  in  the  same  chapter  as  the 
problems  we  have 

C  X  14,600  +  ( H  —  gj  62,000  =  0.6365  X  14,600 

+  (0.0526 ~ - — j  62,000  =  11,773  B.t.u.  per  Ib. 

In  the  second  problem  the  sum  of  the  percentages  of  volatile 
matter  and  fixed  carbon  is 

35.51  +  50.06  =  85.57 

and  dividing  this  into  the  percentage  of  fixed  carbon  and  multiply- 
ing the  quotient  by  100  gives 

ggxxoo-58.5 

the  percentage  of  fixed  carbon  in  the  combustible.  After  locating 
the  58.5  point  at  the  bottom  of  Fig.  n,  in  the  last  lesson,  tracing 
an  imaginary  line  straight  up  to  the  curve  and  then  horizontally 
across  to  the  left  margin,  we  find  that  the  heat  value  per  pound 
of  combustible  matter  is  14,975  B.t.u.  Then,  as  but  85.57  Per 
cent  of  the  coal  in  the  problem  is  combustible  matter,  the  heat 
value  per  pound  of  coal  is 

14,975  X  85.57  -£•  100  =  12,814  B.t.u. 


CHAPTER  III 
FLUE  GAS  ANALYSIS 

Let  us  assume  that  we  have  succeeded  in  discovering  the  best 
coal,  all  things  considered,  for  our  plant.  By  making  proximate 
analyses  and  estimating  heat  values  we  have  found  one  grade  of 
coal  which  has  minimum  moisture  and  ash;  consequently,  it 
gives  maximum  heat-generating  material  per  dollar  invested. 
Upon  actual  trial  in  the  boiler  room  it  is  found  to  work  satis- 
factorily with  the  existing  equipment.  It  does  not  clinker  badly 
and,  hence,  the  firemen  can  handle  it  easily  and  efficiently  and 
maintain  the  stem  pressure  uniform  without  undue  trouble. 

Our  next  problem  is:  How  best  to  burn  this  coal  so  as  to  get 
most  of  the  heat  it  contains  into  the  boiler  and  generate  the  great- 
est quantity  of  steam  possible  per  pound  of  coal  fired.  And  right 
here  is  where  our  knowledge  of  the  underlying  principle  of 
combustion  comes  into  use. 

EXCESS  Ant  NECESSARY 

In  preceding  chapters  it  was  shown  that  each  pound  of  coal  of 
a  certain  composition  requires  a  certain  fixed  weight  of  air  for 
complete  combustion  and  the  method  of  figuring  this  weight  was 
given.  But,  this  theoretically  required  amount  of  air  will  not 
suffice  in  the  boiler  plant  because  if  only  the  required  amount  is 
supplied,  the  distribution  must  be  perfect  so  that  each  particle  of 
oxygen  in  the  air  may  come  in  contact  with  a  particle  of  carbon 
or  hydrogen.  If  this  does  not  take  place,  some  of  the  oxygen 
will  escape  without  combining  with  its  allotted  share  of  the 
combustible  matter,  with  the  result  that  either  of  the  two  following 
things  may  happen:  Some  of  the  hydrogen  may  escape  unburned, 
or  some  of  the  carbon  may  be  only  partly  burned  and  form  CO 
instead  of  CO2. 

In  the  boiler  plant  this  perfect  distribution  of  the  oxygen  is 
impossible.  Consequently,  an  excess  quantity  of  air  must  be 
4  49 


SO        FUEL  ECONOMY  AND  CO2  RECORDERS 

supplied  to  the  fuel  in  the  furnace  in  order  that  complete  com- 
bustion of  every  particle  of  the  burnable  matter  may  be  effected 
and  no  loss  suffered  from  combustible  gases  escaping  up  the 
chimney. 

IMPORTANCE  OF  KNOWING  REQUIRED  EXCESS 

Now,  too  much  excess  air  is  equally  or  even  more  detrimental 
to  good  economy  than  too  little.  Assume  a  given  coal  requires 
10  Ib.  of  air  per  Ib.  of  coal  for  complete  combustion  and  that  the 
gases  formed  weigh  10.75  ^.  The  heat  value  of  a  pound  of  this 
coal  is,  say,  10,000  B.t.u.  Immediately  after  combustion  all 
this  heat  is  contained  in  the  10.75  1°-  °f  gases  and  due  to  this  fact 
their  temperature  is  very  high.  We  are  not  ready  just  yet  to 
estimate  how  high,  so  let  us  assume  the  temperature  to  be  3500 
deg.  F.  As  these  intensely  hot  gases  come  in  contact  with  the 
heating  surface  of  the  boiler  and  give  up  their  heat  to  the  water 
within,  their  temperature  falls  until  it  reaches,  say,  500  deg. 
as  the  gases  leave  the  boiler.  The  gases  are  still  much  hotter  than 
was  the  air  and  coal  which  went  to  make  them  up  and  as  they  ob- 
tained their  heat  from  the  coal,  all  the  coal's  heat  did  not  go  into 
the  boiler  to  make  steam,  but  some  was  lost  up  the  chimney. 

Now,  if  20.75  1°-  °f  a"*  were  fed  per  pound  of  coal,  instead  of 
only  the  required  10  Ib.,  double  the  quantity  of  gases  would 
pass  from  the  boiler.  And  as  these  gases  would  escape  up  the 
chimney  at  about  the  same  temperature  as  the  10.75  l°->  tne 
heat  loss  would  be  about  double  that  in  the  first  case.  This  is 
true  because  with  equal  temperature  the  heat  contained  in  21.50 
Ib.  of  gas  is  just  double  the  amount  contained  in  10.75  Ib. 

Thus,  it  is  important  to  discover  just  what  amount  of  excess 
air  is  most  economical  under  the  existing  conditions  in  your 
plant  and  in  order  to  know  this  some  means  must  be  employed 
to  measure  or  calculate  the  air  supply  to  the  boiler. 

ESTIMATING  AIR  SUPPLIED 

Direct  measurement  would  be  difficult  to  make  and  unsatis- 
factory in  accuracy.  A  far  easier  and  more  accurate  means  is  to 


FLUE  GAS  ANALYSIS  51 

analyze  the  flue  gases  and  calculate  the  air  supply  from  this 
analysis  and  the  coal  analysis.  Flue-gas  analysis  is  also  useful 
in  checking  boiler  operation  from  day  to  day  so  as  to  be  sure 
conditions  will  remain  economical. 

Somehow  or  other,  flue-gas  analysis  has  a  very  mysterious  and 
forbidding  sound.  People  are  inclined  to  think  it  is  too  deep  and 
dark  for  them  to  understand  and,  consequently,  many  have  not 
made  the  good  use  of  it  that  they  should.  As  a  matter  of  actual 
fact,  it  is  simple  to  understand  and  easy  to  master. 

APPARATUS  REQUIRED 

A  suitable  apparatus  is  required  for  making  a  flue-gas  analysis. 
Numerous  types  are  on  the  market  all  of  which  have  points  of 
merit.  Most  of  them,  however,  are  based  on  the  Orsat  apparatus 
which  was  designed  by  a  man  of  that  name.  For  this  reason, 
the  principle  and  operation  of  the  Orsat  only  will  be  given  here. 

Following  is  a  list  of  the  essentials  of  a  flue-gas  analyzing  outfit: 

1  standard  Orsat-Muencke  flue-gas  analysis  apparatus $20.00 

2  rubber  gas  bags  for  pipettes  @  500.  each i  .00 

2  large  glass  bottles,  @  500.  each i .  oo 

2  rubber  corks  for  bottles  @  i5c.  each 0.30 

10  ft.  antimony  rubber  tubing  (\  in.)  @  ice i  .00 

10  ft.  of  $  in.  glass  tubing  in  5-ft.  lengths  @  2C o.  20 

4  Mohr's  pinch  cocks  @  8c.  each 0.32 

i  German-glass  funnel  (2-in.  size) o.  10 

i  Ib.  caustic  potash  (purified  sticks) 0.35 

J  Ib.  pyrogallic  acid o. 80 

i  Ib.  commercial  copper  oxide o .  55 

i  Ib.  muriatic  acid 0.30 

10  ft.  copper  wire  No.  10  gage  @  ice i  .00 

Total $26.92 

The  Orsat  determines  the  percentages  by  volume  of  carbon 
dioxide  (CO2),  carbon  monoxide  (CO),  and  oxygen  (02)  in  the 
flue  gases.  It  consists  chiefly  of  three  bottles  (pipettes)  con- 
nected to  a  common  header.  One  contains  caustic  potash  for 
absorbing  the  CO2,  one  potassium  pyrogallate  for  absorbing  the 
oxygen,  and  one  acid  cuprous  chloride  for  absorbing  the  CO. 


52  FUEL  ECONOMY  AND  CO2  RECORDERS 

A  bottle  of  water  is  used  for  forcing  the  sample  into  and  out  of 
the  pipettes,  and  a  burette  is  provided  for  measuring  in  cubic 
centimeters  the  percentage  of  the  respective  gases  contained  in 
the  sample  of  flue  gas. 

UNPACKING  AND  ASSEMBLING  APPARATUS 

The  Orsat  apparatus  is  shipped  knocked-down;  that  is,  the  glass 
parts  are  taken  out  of  position  and  securely  packed  so  as  to  avoid 
breakage.  The  first  thing  to  do,  then,  is  to  get  the  apparatus 
properly  put  together  again.  If  you  purchase  an  Orsat-Muencke, 
the  following  directions  will  serve  as  an  exact  guide.  If  you 
happen  to  purchase  some  other  type  these  directions  may  have  to 
be  modified  slightly,  but  the  modifications  will  be  self-evident 
when  you  come  to  examine  the  parts.  The  directions  I  will  give 
for  preparing  the  chemicals  and  operating  the  apparatus  can  be 
followed  exactly  with  any  of  the  standard  types  of  Orsat. 

After  carefully  unpacking  the  box  in  which  the  apparatus  is 
shipped  and  making  sure  that  you  have  not  missed  anything,  dust 
off  the  cabinet  and  wash  the  glass  parts  with  warm  water  and  soap, 
rinsing  thoroughly  in  clean  water  at  the  end.  Take  both  front 
and  back  slides  out  of  the  cabinet  and  place  it  before  you  so  that 
the  long,  narrow  compartment  is  at  the  right. 

Next,  put  the  header  A,  Fig.  12,  in  position,  first  making  sure 
that  the  five  rubber  connectors  B  are  in  place  ready  to  make  the 
connection  between  the  header  and  the  other  parts.  The  header 
is  held  in  place  by  the  small  wooden  latch  C\  be  sure  that  this  is 
in  the  closed  position  before  proceeding. 

The  next  step  is  to  fit  the  burette  or  measuring  chamber  D 
into  position.  This  burette  is  provided  with  an  outer  case  E,  of 
glass,  for  the  purpose  of  preventing  error  due  to  change  in  the 
temperature  of  the  air  in  the  room  affecting  the  gas  in  the  burette. 
The  space  between  the  outside  case  and  the  burette  should  be 
filled  with  clean  water.  As  the  rubber  corks  F  both  contain  vent 
holes,  the  one  in  the  bottom  cork  will  have  to  be  plugged  up  after 
the  water  is  run  in.  See  that  the  white  side  of  the  case  with  the 
blue  stripe  down  the  middle  comes  on  the  side  opposite  to  the 


FLUE  GAS  ANALYSIS 


S3 


scale  marks  on  the  burette.  This  white  and  blue  background 
makes  it  easier  to  read  the  water  level  in  the  burette  when 
measuring. 

Having  the  casing  filled  with  water,  the  next  step  is  to  connect 
the  burette  with  the  header  at  the  top.  Put  the  two  small  sliding 
shelves  G  over  the  stems  H  and  Hr  and  fit  the  shelves  into  their 
grooves.  This  will  hold  the  burette  in  position  so  that  you  can 


B 


FIG.  12. — Diagram  for  assembling  orsat. 

use  both  hands  for  slipping  the  rubber  connector  over  the  stem. 
Be  sure  that  the  stem  is  moistened  with  water  as  this  will  make 
the  rubber  slide  much  more  easily.  Draw  the  top  shelf  out  a 
little  so  that  the  stem  does  not  come  directly  under  the  header 
end,  then  gently  work  the  rubber  connector  over  the  stem  until 
it  fits  snugly  with  the  weight  of  the  burette  resting  on  the  bottom 


54        FUEL  ECONOMY  AND  CO2  RECORDERS 

shelf.  This  will  keep  strain  off  the  header.  Great  care  will  be 
necessary  in  the  making  of  these  connections  as  the  use  of  too 
much  force  will  result  in  breakage. 

Two  pieces  of  rubber  tubing  come  with  the  apparatus.  The 
longer  piece  is  for  making  the  connection  between  the  burette 
and  the  leveling  bottle  7.  Before  making  this  connection,  slip 
one  of  the  pinch  cocks  on  the  tubing,  as  this  will  come  in  handy  to 
regulate  the  water  level  when  making  analyses. 

Next,  the  pipettes  /,  K  and  L  are  put  into  place.  These 
pipettes  consist  of  two  bottle-like  parts  connected  at  the  bottom 
by  means  of  a  glass  neck.  The  construction  of  the  pipettes 
varies  somewhat  with  different  apparatus.  Some,  such  as  / 
and  K,  have  the  stem  M  connected  solidly  to  the  bottle  part  while 
with  others,  such  as  L,  the  stem  forms  part  of  a  stopper  which 
makes  a  ground-glass  fit  with  the  neck  of  the  bottle  part. 

A  number  of  small  glass  tubes  are  furnished  to  insert  in  the  front 
leg  of  each  pipette.  These  tubes  may  come  already  in  place. 
If  so,  there  may  be  some  cotton  wedged  into  the  bottle  above 
them  to  prevent  them  rattling  and  possibly  becoming  broken  in 
shipment.  This  cotton  must  all  be  removed.  If  the  tubes  do 
not  arrive  already  in  place  fill  the  front  leg  of  two  pipettes  as  full 
as  you  can  with  the  plain  tubes  and  the  front  leg  of  the  third 
pipette  with  the  tubes  which  have  little  spirals  of  copper  wire  in 
them.  Be  sure  that  the  pipettes  are  arranged  in  the  cabinet  in 
the  proper  order;  the  two  nearest  to  the  burette  should  contain 
the  plain  glass  tubes  while  the  farthest  one  should  contain  the 
tubes  with  the  copper  spirals.  In  time  these  copper  spirals  will 
become  dissolved  by  the  solution  used  in  this  pipette  .and  new 
tubes  containing  spirals  will  have  to  be  purchased  and  put  in. 

Into  the  back  leg  of  each  pipette  fit  a  goose-neck  stopper,  as 
shown  in  Fig.  13,  and  to  the  goose-necks  of  the  two  pipettes 
furthest  away  from  the  burette  attach  the  rubber  gas  bags,  as 
shown  in  Fig.  14.  The  object  of  these  bags  is  to  prevent  air  from 
coming  in  contact  with  the  chemicals  in  the  pipettes  and  spoiling 
them.  The  chemical  in  the  first  pipette  need  not  be  so  protected. 

The  U-tube  O,  Fig.  12,  is  next  attached  to  the  end  of  the  header, 


FLUE  GAS  ANALYSIS  55 

as  shown,  and  the  apparatus  is  ready  to  load  and  use.  This 
U-tube  has  a  wad  of  mineral  wool  in  its  open  end  and  serves  as  a 
filter  for  the  gases  before  they  enter  the  apparatus,  catching  any 


POWE.R 


FIG.  13. — Front  view  of  assembled  apparatus. 

particles  of  dust  and  soot  which  might  otherwise  foul  up  the  header 
and  cause  trouble  in  the  glass  cocks.     It  also  can  be  filled  with 


56  FUEL  ECONOMY  AND  CO2  RECORDERS 

small  lumps  of  calcium  chloride  for  absorbing  moisture  from  the 
gases.     This,  however,  is  not  absolutely  necessary. 

I  would  advise  all  beginners  to  practice  loading  and  manipulat- 
ing the  apparatus  with  plain  water  before  putting  in  the  chemi- 


POVLR 


FIG.  14. — Rear  view  of  assembled  apparatus. 

cals,  as  the  latter  are  nasty  to  spill  or  slop  around  as  well  as 
somewhat  too  expensive  to  deliberately  waste.      So,  until  you 


FLUE  GAS  ANALYSIS  57 

fully  understand  how  the  analysis  is  conducted,  plain  water  is  the 
safest  and  cheapest  material  to  experiment  with. 


LOADING  APPARATUS 

The  correct  amount  of  chemical  must  be  put  into  each  pipette 
or  otherwise  the  apparatus  will  not  work  well.  Remove  the  goose- 
neck from  the  rear  leg  of  the  pipette  and  add  the  chemical  through 
the  glass  funnel  until  the  two  legs  are  slightly  more  than  half  full. 
In  order  that  the  liquid  may  rise  equally  in  both  legs  the  stop 
cock  in  the  front  connection  must  be  open  and  also  the  three-way 
cockP  in  the  header,  Fig.  12,  must  be  open  to  the  atmosphere. 
After  you  have  filled  one  pipette  /,  for  instance,  tested  it  and 
found  it  to  contain  the  proper  quantity  of  liquid,  it  is  an  easy 
matter  to  get  the  other  two  correct  simply  by  filling  them  to  the 
same  level. 

To  test  whether  pipette  J  contains  the  right  quantity  of  liquid, 
fill  the  leveling  bottle  /  about  two-thirds  full  of  water,  first  closing 
the  pinch  cock  R.  See  that  all  the  glass  cocks  connecting  with 
the  header  are  closed  except  cock  Q,  which  must  remain  open. 
Now,  raise  the  leveling  bottle  and  place  it  on  top  of  the  cabinet 
as  at  /'.  Then,  press  the  buttons  of  the  pinch  cock  R  until  the 
water  begins  to  rise  in  the  burette.  This  places  the  air  trapped 
above  the  water  in  the  burette  and  in  the  header  under  a  slight 
pressure  and  as  the  stop  cock  Q  is  open  this  pressure  is  com- 
municated to  the  front  leg  of  the  pipette  7,  driving  the  liquid 
down  in  this  leg  and  up  in  the  back  leg.  By  regulating  the 
pressure  of  your  fingers  on  the  pinch  cock  R  you  can  control  the 
flow  very  nicely.  If  the  pipette  contains  the  correct  amount  of 
liquid,  by  the  time  the  liquid  has  gone  down  in  the  front  leg  to  the 
point  where  the  body  part  begins  to  narrow  into  the  bottom- 
connecting  tube,  the  liquid  in  the  back  leg  will  have  risen  to  the 
point  where  the  body  part  begins  to  narrow  into  the  neck  at  the 
top. 

If  too  much  liquid  has  been  put  into  the  pipette,  the  back  leg  will 
be  full  or  overflowing  before  the  front  leg  has  been  emptied  to  the 


58  FUEL  ECONOMY  AND  CO2  RECORDERS 

point  mentioned  in  the  preceding  paragraph,  and  some  of  the 
liquid  will  have  to  be  removed.  If  not  enough  liquid  has  been  put 
in,  air  will  force  its  way  through  the  bottom  connection  and  bubble 
up  through  the  liquid  in  the  back  leg.  To  prevent  this,  more 
liquid  must  be  added. 

EMPTYING  PIPETTES 

After  the  apparatus  has  been  used  for  some  time,  the  chemicals 
become  weak  and  must  be  renewed.  A  convenient  way  of  empty- 
ing a  pipette  is  to  fill  a  short  length  of  rubber  tubing  (about  2  ft. 
long)  with  water,  and  while  holding  your  finger  over  one  end,  to 
prevent  the  water  from  running  out,  put  the  other  end  into  the 
back  leg  of  the  pipette.  Then,  lower  the  free  end  into  a  sink  or 
basin  so  that  this  end  is  somewhat  below  the  other  and  release 
your  finger,  when  the  liquid  will  all  siphon  out  of  the  pipette. 

PREPARING  FOR  AN  ANALYSIS 

After  all  three  pipettes  have  been  properly  filled  and  tested  the 
apparatus  is  almost  ready  for  making  analyses.  Before  it  is 
quite  ready,  however,  the  liquid  in  each  pipette  must  be  drawn 
up  into  the  front  leg  until  this  leg  is  full  to  the  fine  black  ring, 
which  will  be  found  around  the  neck  at  S. 

To  do  this  in  the  case  of  pipette  /,  notice  whether  the  water 
level  in  the  burette  D  is  near  the  top.  If  it  is  not,  close  all  the 
header-connection  cocks  except,  the  threeway  cock  P,  which  must 
be  open.  Then,  raise  the  leveling  bottle  to  /'  and  allow  the  water 
level  to  rise  in  the  burette  by  opening  the  pinch  cock  R.  When 
the  water  level  in  the  burette  is  right,  close  the  three-way  cock 
and  open  stop-cock  Q.  Lower  the  leveling  bottle  to  the  table  and 
by  releasing  pinch  cock  R  allow  the  water  in  the  burette  to  run 
back  into  the  bottle;  while  doing  so,  watch  the  liquid  rise  in  the 
front  leg  of  /.  When  this  is  near  the  top,  proceed  very  slowly 
and  carefully  as  the  necks  M  (made  of  what  is  known  as  capillary 
tubing)  have  a  very  fine  bore,  and  if  you  allow  the  liquid  to  rise 


FLUE  GAS  ANALYSIS  59 

too  rapidly  when  near  the  top,  there  is  considerable  danger  that  it 
will  shoot  up  into  the  header  and  over  into  the  burette  before  you 
can  check  it.  While  this  will  do  no  harm  when  practising  with 
water,  it  is  undesirable  when  dealing  with  the  chemicals,  as  it 
makes  the  water  in  the  burette  more  or  less  capable  of 
absorbing  the  flue  gases,  thus  causing  error,  and  it  reduces  the 
quantity  of  liquid  in  the  pipette  so  that  trouble  may  arise  in  this 
direction  also. 

The  proceeding  for  bringing  the  liquid  in  pipettes  K  and  L  up 
to  the  mark  is  exactly  the  same  as  for  pipette  /,  only,  while  doing 
so,  it  is  advisable  to  remove  the  goosenecks  with  the  rubber  bags 
attached,  from  the  mouth  of  the  back  legs,  for  unless  there  hap- 
pens to  be  enough  air  in  these  bags,  a  vacuum  may  be  formed  over 
the  liquid  in  the  back  leg,  thereby  preventing  it  from  coming 
fully  up  to  the  mark  in  the  front  leg  as  it  should.  As  soon  as  the 
liquid  has  been  brought  up  to  the  mark,  replace  the  goosenecks 
and  rubber  bags  to  prevent  further  contact  with  the  outside  air. 
When  dealing  with  the  chemicals,  the  air  that  it  trapped  in  the  back 
leg  of  K  and  L  will  lose  its  oxygen,  and,  hence,  shrink  in  volume  so 
that  a  slight  vacuum  will  be  formed.  When  this  noticeably  inter- 
feres with  the  operation  of  the  apparatus,  remove  the  gooseneck 
for  an  instant  to  let  in  a  little  more  air.  Be  sure  to  do  this,  how- 
ever,when  the  liquid  is  up  to  the  mark  in  the  front  leg  or  when  the 
gas  bag  is  perfectly  flat  or  empty,  as  otherwise,  instead  of  letting 
more  air  into  the  system,  you  will  really  let  some  out  and  cause  a 
worse  vacuum  than  ever. 

A  better  way  to  avoid  trouble  from  the  formation  of  a  vacuum 
is  to  force  a  little  excess  air  into  the  bag  by  blowing  into  it  with 
your  mouth,  then,  pinching  the  neck  to  hold  the  air  in  until  the 
connection  is  made.  It  is  well  to  take  precaution,  however,  when 
doing  this,  and  be  sure  that  there  is  none  of  the  chemical  on  the 
end  you  put  to  your  lips,  as  otherwise  you  may  burn  yourself. 

With  the  liquid  in  all  pipettes  properly  adjusted,  an  analysis 
can  now  be  made.  That  is,  we  can  go  through  the  motions  of 
making  an  analysis.  Later,  when  more  practice  has  been 
gained,  we  will  load  with  the  proper  chemicals  and  after  making 


60        FUEL  ECONOMY  AND  CO2  RECORDERS 

suitable  arrangements  for  obtaining  a  sample  of  the  flue  gases,  we 
will  be  prepared  for  actual  work. 

VOLUME  OF  SAMPLE 

For  the  present,  assume  that  the  filter  O  is  connected  with  the 
supply  of  gas.  Our  sample  will  consist  of  100  c.c.  of  flue  gas  at 
atmospheric  pressure  and  at  the  temperature  of  the  ordinary  room 
air. 

At  its  lower  part,  where  all  our  readings  will  be  taken,  the 
burette  is  graduated  in  cubic  centimeters  with  a  subdivision  for 
each  0.2  of  a  cubic  centimeter.  Thus,  the  figures  of  the  scale  read 
direct  in  per  cents,  and  decimal  fractions  of  a  per  cent. 

A  cubic  centimeter  is  another  French  or  metric  unit  employed 
because  of  its  great  convenience,  like  the  gram,  decigram  and  milli- 
gram in  our  proximate  coal  analysis.  The  metric  units  of  length, 
corresponding  with  inches,  feet  and  yards,  are  the  centimeter, 
decimeter  and  meter.  Consequently,  the  units  of  volume  are  the 
cubic  centimeter,  cubic  decimeter  and  cubic  meter.  Do  not  fall 
into  the  mistake,  however,  of  assuming  that  100  c.c.  equals  i 
cu.  m.  for  they  do  not — no  more  than  12  cu.  in.  equal  i 
cu.  ft.  At  the  bottom  of  the  scale  on  the  Orsat  burette  you 
will  find  the  letters  c.c.,  which  is  the  standard  abbreviation  for 
cubic  centimeter. 

EFFECT  OF  TEMPERATURE  AND  PRESSURE 

You  may  have  noticed  that  I  specified  that  our  gas  sample  was 
to  be  at  a  certain  pressure  and  temperature.  This  is  because  the 
volume  of  a  gas  is  greatly  influenced  by  changes  in  pressure  and 
temperature.  Hence,  we  must  be  careful  to  have  conditions 
uniform  throughout  an  analysis,  or  error  wih1  result.  It  is  advis- 
able for  best  results  to  locate  the  apparatus  where  no  drafts  will 
blow  on  it  and  where  the  temperature  of  the  air  does  not  change 
rapidly. 

To  illustrate  how  important  an  influence  temperature  and  pres- 
sure have,  two  simple  experiments  can  be  made  with  your  Orsat. 

To  show  the  effects  of  change  in  temperature,  locate    the 


FLUE  GAS  ANALYSIS  6 1 

apparatus  in  a  warm  spot  and  allow  it  to  remain  there  for  about 
an  hour,  until  the  glass  work  and  the  water  come  up  to  the 
temperature  of  the  air.  Then,  with  all  cocks  closed  except  P, 
which  must  be  open,  slowly  raise  or  lower  the  leveling  bottle, 
using  the  side  of  the  cabinet  as  a  guide,  until  the  water  level  in  the 
burette  D  is  exactly  on  the  zero  mark,  while  at  the  same  time  the 
water  level  in  the  bottle  is  at  the  same  height  as  the  water  level 
in  the  burette,  as  shown  by  the  position  of  the  bottle  at  I". 
Then,  using  care  not  to  change  the  level  of  the  bottle,  close  cock 
P.  To  make  sure  that  no  mistake  has  been  made  while  closing 
the  cock  P,  check  the  water  levels  once  more  by  noting  whether 
both  are  at  the  level  of  the  zero  mark.  If  not,  and  if  they  cannot 
be  brought  right  by  a  slight  raising  or  lowering  of  the  bottle,  open 
the  cock  P  and  start  all  over  again. 

Having  thus  succeeded  in  getting  the  correct  quantity  of  warm 
air  into  the  burette,  place  the  leveling  bottle  in  its  cleat  within  the 
cabinet  at  /' "  and  shift  the  apparatus  to  some  spot  where  the 
temperature  is  10  or  15  deg.  cooler.  After  about  an  hour's  time, 
test  the  water  level  again  (without  opening  cock  P)  by  slowly 
raising  and  lowering  the  leveling  bottle  at  the  side  of  the  cabinet 
until  the  level  in  the  bottle  is  the  same  as  the  level  in  the  burette. 
This  new  level  will  be  considerably  above  the  zero  mark,  showing 
that  the  reduction  in  temperature  caused  the  volume  of  the  air  in 
the  burette  to  shrink.  A  reduction  in  temperature  of  10  deg. 
means  a  reduction  in  volume  of  about  1.8  per  cent. 

To  show  the  effect  of  change  in  pressure,  open  cock  P  and  by 
raising  or  lowering  the  leveling  bottle,  draw  in  enough  air  to  bring 
the  water  level  to  about  the  10  per  cent.  mark.  Close  cock  P 
and  make  an  accurate  reading  by  raising  or  lowering  the  bottle 
until  the  water  level,  is  the  same  in  the  bottle  and  in  the  burette. 
Now,  if  you  raise  the  bottle,  say,  to  position  /',  the  water  level  in 
the  burette  will  rise  almost  to  the  14  per  cent.  mark.  This  shows 
that  the  tendency  of  the  water  in  the  bottle  to  flow  into  the 
burette  and  seek  its  own  level  has  put  an  increase  of  pressure  on 
the  air  trapped  in  the  burette  and,  hence,  has  reduced  its  volume 
by  compression. 


62  FUEL  ECONOMY  AND  CO2  RECORDERS 

MANIPULATION  OF  THREE-WAY  COCK 

Thus  far,  I  have  said  nothing  about  the  manipulation  of  the 
three-way  cock  P.  Its  correct  manipulation  is  very  important 
when  making  an  actual  analysis,  and  as  a  poor  understanding  of 
how  it  should  be  handled  would  undoubtedly  lead  to  confusion 
and  inaccuracy  in  results,  it  is  worth  devoting  a  paragraph  at  this 
point  to  this  important  part  of  the  machine. 

Fig.  15  is  a  diagram  of  the  three-way  cock  connection.  The 
straight-run  passage  XY  is  parallel  with  the  handle  of  the  cock 
and  the  branch  connection  Z  is  on  the  same  side  as  a  dark  dot 
found  on  the  handle.  In  the  position  shown  in  Fig.  15  (in  which 
position  the  handle  would  be  horizontal  and  the  dot  would  be 
facing  down)  the  gas  supply,  the  outside  air  and  the  burette, 
would  all  be  connected. 

In  the  reverse  position  (with  handle  horizontal  and  dot  facing 
up)  only  the  gas  supply  and  the  burette  would  be  connected. 

With    the  handle    in    a    vertical 
position  and  the  dot  facing  to  the 
left  the  gas  supply  and  the  out- 
side   air    would    be    connected. 
With  the  handle  vertical  and  the 
dot  to  the  right,  the  burette  and 
FlG<  l5._Diagram  of  three-way      the     air    would    be     connected. 
cock-  With   the   handle  in  any  45~deg. 

position  no  connections  would  be  open. 

Assume  that  the  apparatus  is  conected  with  the  gas  supply. 
Connect  the  burette  with  the  atmosphere  by  setting  the  three-way 
cock  with  the  dot  on  the  handle  facing  to  the  right.  Then,  place 
the  leveling  bottle  on  top  of  the  cabinet  and  drive  all  the  air  out 
of  the  burette  by  opening  the  pinch  cock  R,  Fig.  9,  and  allowing 
the  water  to  run  in  until  it  reaches  the  loo-c.c.  mark  on  the 
upper  neck  H.  Now,  turn  the  three-way  cock  so  that  the  dot 
faces  up,  thus  connecting  the  burette  and  gas  supply.  Lower  the 
leveling  bottle  and  release  the  pinch  cock  R  entirely  from  the 
rubber  connection.  Then,  connect  the  small  hand  pump  to  the 


FLUE  GAS  ANALYSIS  63 

leveling  bottle  in  the  manner  shown  in  Fig.  12  and  start  pumping. 
If  the  gas  is  being  drawn  direct  from  the  flue  or  chimney  be  sure 
that  you  pump  long  enough  to  secure  a  burette  full  of  true 
gas.  The  amount  of  pumping  required  depends  upon  the  length 
of  the  connection  between  the  apparatus  and  the  flue.  After  a 
little  experience  you  will  be  able  to  tell  just  about  how  much 
pumping  is  required.  Remember,  however,  it  is  far  better  to 
pump  a  little  longer  than  is  actually  necessary  than  not  to 
pump  quite  long  enough.  If  the  gas  is  being  drawn  from  some 
kind  of  collecting  apparatus,  only  a  few  strokes  of  the  pump 
will  be  needed — say,  a  half  dozen. 

When  you  feel  sure  the  burette  is  full  of  real  gas,  cease  pumping 
and  immediately  give  the  three-way  cock  one-eighth  turn  to  the 
right  so  that  the  handle  is  at  45  deg.  and  the  dot  is  still  on  the 
upward  side.  Then,  put  the  pinch  cock  on  the  leveling-bottle 
hose  at  about  6  in.  from  the  burette  end,  disconnect  the  hand 
pump,  and  place  the  bottle  on  top  of  the  cabinet.  Now,  open  the 
three-way  cock  to  the  air  by  giving  it  another  eighth  turn  to  the 
right  and  by  carefully  releasing  the  pinch  cock  from  the  leveling- 
bottle  hose,  run  the  water  into  the  burette  to  exactly  the  zero 
mark.  If,  by  accident,  you  permit  the  water  to  rise  above  the 
zero  mark,  do  not  attempt  to  bring  it  back  by  means  of  the 
leveling  bottle,  for  this  would  only  let  air  into  the  burette  and 
spoil  the  sample.  If  you  wish,  you  can  proceed  with  the  analysis 
and  make  correction  by  calculation  afterward,  but  I  consider  it 
better  to  simply  expel  all  the  gas  and  start  over  again.  This 
avoids  chance  for  error  later  and  is  about  as  quick  as  if  you  took 
the  time  to  calculate  the  correction. 


TESTING  FOR  CC>2 

As  soon  as  the  water  is  brought  up  to  the  zero  mark,  close  the 
three-way  cock  by  giving  it  an  eighth  turn  to  the  left,  and  open 
the  cock  Q,  on  the  first  pipette.  Squeeze  the  pinch  cock  on  the 
leveling-bottle  hose  and  allow  the  water  to  rise  in  the  burette  to 
or  nearly  to  the  loo-c.c.  mark.  This  forces  the  gas  over  into  the 


64  FUEL  ECONOMY  AND  CO2  RECORDERS 

pipette  /,  the  gas  driving  the  liquid  from  the  front  leg  of  the 
pipette  into  the  back.  All  the  little  glass  tubes  in  the  front  leg 
are  now  exposed  to  the  gas  and  as  they  are  dripping  with  the  solu- 
tion just  driven  out,  they  present  a  large  wetted  surface,  and, 
hence,  hasten  the  chemical  action  between  the  solution  and  the 
gas. 

Allow  the  gas  to  remain  in  the  pipette  about  one  minute,  then 
draw  it  back  into  the  burette  by  lowering  the  leveling  bottle  and 
releasing  the  pinch  cock,  using  ca*e  that  none  of  the  solution  is 
drawn  over  with  it.  Repeat  this  operation  about  three  times 
and  then  measure  the  gas  as  follows:  Draw  the  solution 
in  the  pipette  up  to  the  mark  S  on  the  stem  and  close  the 
cock  Q.  Then,  release  the  leveling-bottle  hose  entirely  from  the 
pinch  cock  and  make  the  water  level  in  the  burette  and  bottle 
equal  by  raising  or  lowering  the  bottle  at  the  side  of  the  cabinet 
as  before  described.  Read  the  mark  at  which  the  water  now 
stands  in  the  burette.  If,  for  instance,  the  water  now  stands  at 
the  8.2-c.c.  mark,  the  volume  of  the  gas  has  diminished  8.2  c.c. 
in  100,  or  8.2  per  cent.,  and  that  is  the  percentage  of  CC>2  in  the 
flue  gas.  The  solution  in  the  first  pipette  takes  out  (or  absorbs) 
the  CO2,  leaving  the  oxygen,  carbon  monoxide  and  nitrogen. 

CHECKING  RESULTS 

After  making  the  reading,  run  the  gas  into  the  pipette  once 
more  and  take  another  reading  as  a  check  to  make  sure  that  all 
the  CO2  has  been  absorbed.  If  both  readings  are  the  same,  all 
right.  If  not,  make  one  more  trial.  When  reading  for  CO2 
you  should  have  no  trouble  in  getting  the  first  two  readings  to 
agree.  If  you  do  have  trouble,  your  method  may  be  wrong  and 
it  may  be  necessary  to  allow  the  gas  to  stand  in  the  pipette  a  little 
longer  each  time  or  to  increase  the  number  of  times  you  run  it 
back  and  forth.  Or,  if  the  solution  has  been  used  a  long  time  it 
may  have  become  weak  and  need  renewing. 

A  good  thing  to  remember  when  running  the  gas  from  the 
burette  into  the  pipette  zndvice  versa  is  to  watch  the  rising  liquid, 


FLUE  GAS  ANALYSIS  65 

in  this  way  eliminating  the  danger  of  running  any  liquid  out  of 
the  vessel  in  which  it  belongs.  Thus,  when  running  the  gas  from 
the  burette  into  the  pipette,  watch  the  water  rise  in  the  burette, 
stopping  the  flow  before  it  shoots  up  through  the  neck  H,  and  over 
through  the  header  into  the  pipette.  When  running  the  gas 
back,  watch  the  liquid  rise  in  the  front  leg  of  the  pipette  and  stop 
it  before  it  reaches  the  burette. 

TESTING  FOR  OXYGEN 

After  getting  a  check  on  the  C(>2  reading,  open  the  cock  on 
pipette  K,  and  run  the  gas  back  and  forth  in  this  pipette  in 
exactly  the  same  manner  as  before.  Only,  instead  of  running 
it  in  and  out  only  four  times,  as  in  the  case  with  the  first  pipette, 
the  operation  should  be  repeated  about  seven  times  before  a 
reading  is  taken.  The  reason  for  this  is  that  the  solution  for 
absorbing  oxygen,  the  part  of  the  flue  gas  absorbed  in  the  second 
pipette,  does  not  act  as  quickly  as  the  solution  used  in  the  first 
pipette  for  absorbing  CO2. 

Check  the  reading  in  the  same  manner  as  before  by  running 
the  gas  over  once  more  and  taking  an  extra  reading.  The 
difference  between  the  new  correct  reading  and  the  first  correct 
reading  gives  the  percentage  of  oxygen  contained  in  the  flue  gas. 
For  instance,  if  the  new  reading  were  17.6  per  cent,  and  the  previ- 
ous one  had  been  8.2  per  cent.,  then  the  oxygen  content  in  the  flue 
gas  would  be 

17.6  —  8.2  =5  9.4  per  cent. 

TESTING  FOR  CO 

After  obtaining  a  correct  reading  for  the  oxygen,  open  the 
cock  on  pipette  L  and  go  through  the  same  process  with  this 
pipette  as  with  the  other  two,  only  repeat  the  operation  of  running 
the  gas  back  and  forth  about  n  times.  The  solution  in  this 
pipette  absorbs  any  carbon  monoxide  (CO)  that  may  be  con- 
tained in  the  flue  gas.  Its  action,  however,  is  very  slow  and  feeble 
and  much  care  and  patience  must  be  used  to  get  a  correct  reading. 


66        FUEL  ECONOMY  AND  CO2  RECORDERS 

The  principle  upon  which  the  Orsat  apparatus  is  based  is  that 
when  certain  chemical  solutions  are  brought  in  contact  with 
certain  gases,  the  gases  combine  chemically  with  the  solutions 
in  such  a  way  that  they  become  a  part  of  the  solution.  Ordinary 
flue  gas  consists  principally  of  a  mixture  of  carbon  dioxide,  oxygen 
and  nitrogen  and,  sometimes,  carbon  monoxide,  hydrogen  and 
some  hydrocarbons.  When  a  given  volume  of  such  a  mixture  is 
brought  in  contact  with  a  solution  of  caustic  potash  and  water, 
the  carbon  dioxide  combines  with  the  caustic  potash  and  forms 
a  substance  which  becomes  a  part  of  the  solution.  The  solution 
increases  in  volume  but  very  slightly  indeed — so  slightly,  in  fact, 
that  the  increase  may  be  entirely  neglected  in  our  work.  But 
the  volume  of  the  flue  gas  has  diminished  by  the  amount  of  carbon 
dioxide  it  contained. 

In  a  similar  way  the  oxygen  and  the  carbon  monoxide  disap- 
pear from  the  flue  gas  when  brought  into  contact  with  the  proper 
chemical  solutions. 

The  solutions  used  in  the  Orsat  must  be  employed  in  the 
order  here  given  because  the  solution  for  carbon  monoxide  will 
absorb  oxygen  as  well,  and  the  solution  for  oxygen  will  absorb 
carbon  dioxide,  so  the  CO2  must  be  taken  out  first,  the  oxygen 
second  and  the  CO  third. 


SOLUTION  FOR  CO2 

The  solution  for  the  first  pipette,  to  absorb  the  C02,  is  caustic 
potash  (chemical  name,  potassium  hydrate)  dissolved  in  the 
proportion  of  i  Ib.  of  caustic  to  i\  Ib.  (i\  pints)  of  water. 

Perhaps  the  most  convenient  method  is  to  mix  up  \  Ib.  of 
the  caustic  at  a  time.  A  good  way  to  do  is  to  fill  an  ordinary  i- 
quart  milk  bottle  about  five-eighths  full  of  water  and  add  half 
of  the  sticks  in  a  i-lb.  package  of  caustic.  If  you  have  a 
pair  of  reasonably  accurate  small  scales,  you  can  weigh  the 
bottle  and  then  add  the  required  i \  Ib.  of  water,  thus  securing 
greater  accuracy  than  guessing  at  five-eighths  of  a  quart.  A  half 
pound  of  caustic  will  make  a  little  more  than  enough  solution 


FLUE  GAS  ANALYSIS  67 

for  five  loadings  of  the  pipette.  And  one  loading  of  the  pipette 
is  sufficient  for  about  325  analyses  where  the  percentage  of  CO2 
extracted  each  time  is  12  per  cent.  Thus,  one  loading  should 
last  from  three  months  to  a  year  or  more,  depending  on  how  often 
the  apparatus  is  used.  The  bottle  containing  the  unused  part  of 
the  mixture  should  be  carefully  labeled,  fitted  with  a  cork  or  cover 
and  stored  away  in  a  safe  place.  It  is  safest  to  handle  the  potash 
sticks  with  tongs  rather  than  with  the  bare  hands  because  while 
no  harm  will  be  done  if  both  the  sticks  and  your  hands  are  dry,  a 
disagreeable  burn  results  if  either  happens  to  be  moist.  Use  care 
in  handling  the  solution  when  made  up  because  a  drop  on  the  flesh 
will  burn  and  a  drop  on  clothing,  shoes,  etc.,  will  eat  a  hole. 

SOLUTION  FOR  OXYGEN 

The  solution  for  the  second  pipette,  to  absorb  the  oxygen,  is 
potassium  pyrogallate;  made  by  mixing  pyrogallic  acid  (which 
comes  in  the  form  of  a  powder)  with  a  suitable  quantity  of  the 
caustic-potash  solution  just  described.  As  this  solution  absorbs 
oxygen  it  will  quickly  lose  strength  if  exposed  to  the  air;  hence 
it  must  be  sealed  up  as  soon  as  possible. 

A  good  way  to  mix  the  solution  is  to  put  i  oz.  of  the  pyrogallic 
acid  into  a  quart  bottle,  pour  in  about  a  pint  of  the  caustic  solu- 
tion and  immediately  seal  the  bottle  air-tight. 

After  loading  the  pipette,  place  the  gooseneck  and  rubber  bag 
on  the  back  leg  as  quickly  as  possible  to  exclude  the  air.  One 
loading  of  the  pipette  will  absorb  about  200  c.c.  of  oxygen.  Thus, 
if  the  average  amount  of  oxygen  in  the  flue  gases  analyzed  is,  say, 
8  per  cent.,  the  solution  would  be  good  for  about  25  analyses. 

SOLUTION  FOR  CO 

The  solution  for  the  third  pipette,  to  absorb  the  CO,  is  acid 
cuprous  chloride.  This  can  be  most  conveniently  made  as  fol- 
lows: Put  enough  copper  oxide  into  a  quart  bottle  to  make  a 
layer  on  the  bottom  J  in.  thick.  Put  in  ten  or  a  dozen  lengths 
of  No.  10  gage  copper*  wire,  bare  and  clean,  cut  in  lengths  to  reach 
from  the  top  to  the  bottom  of  the  bottle.  Then  fill  the  bottle 


68        FUEL  ECONOMY  AND  CO2  RECORDERS 

with  hydrochloric  acid  (hydrochloric  acid  is  simply  equal  parts 
water  and  muriatic  acid).  Seal  the  bottle  air-tight  and  shake  it 
occasionally  to  hasten  the  reaction.  When  the  solution  turns 
nearly  colorless  (after  about  48  hr.)  it  is  ready  to  use.  After 
some  of  the  solution  has  been  taken  out  to  load  the  pipette, 
immediately  add  more  hydrochloric  acid  so  as  to  keep  the  bottle 
full  all  the  time.  As  the  copper  wire  and  copper  oxide  gradually 
disappear,  add  some  of  each  from  time  to  time  so  as  to  constantly 
keep  about  the  usual  amount  in  the  bottle. 

As  this  solution  also  deteriorates  when  exposed  to  the  air,  be 
sure  to  connect  the  rubber  bag  to  the  pipette  as  soon  as  it  is 
loaded.  One  loading  of  the  pipette  will  absorb  about  100  c.c. 
of  CO;  hence  it  would  be  good  for  about  100  analyses  wrhere  the 
amount  of  CO  in  the  flue  gas  averaged  i  per  cent. 

When  any  of  the  solutions  begin  to  show  signs  of  weakness 
they  should  immediately  be  renewed  regardless  of  the  length  of 
time  they  have  been  in  use. 

TAKING  THE  SAMPLE 

The  best  place  from  which  to  take  the  sample  of  flue  gas  is 
from  the  last  pass,  if  the  boiler  is  a  water-tube,  or  from  the 
connection  between  boiler  and  breeching  if  a  fire-tube.  Cut  a 
length  of  J-in.  pipe  T,  Fig.  16,  long  enough  to  extend  half  way 
across  the  gas  passage  and  project  out  about  6  in.  at  one  side. 
Fit  an  elbow  and  vertical  connection  to  this  as  shown.  The  pipe 
T  may  be  inserted  either  through  a  drilled  hole  or  through  some 
existing  opening.  In  either  case,  stop  up  the  hole  or  opening 
around  the  pipe  with  waste  or  plastic  asbestos  so  as  to  prevent 
the  danger  of  air  leaking  in  and  spoiling  the  sample.  Be  sure 
that  the  piping  is  made  up  air-tight.  Draw  the  end  U  down  so 
that  J-in.  rubber  tubing  can  be  pushed  over  it. 

If  instantaneous  flue-gas  readings  are  wranted,  connect  the 
Orsat  and  the  end  U  by  a  length  of  rubber  tubing  and  proceed 
to  draw  in  the  sample  as  before  directed. 

If  a  sample  representing  a  certain  period  of  operation  is  de- 
sired, an  arrangement,  such  as  shown  in  Fig.  16,  may  be  used. 


FLUE  GAS  ANALYSIS  69 

Obtain  two  large  bottles,  such  as  those  in  which  spring  water  is 
sold,  and  fit  them  with  rubber  corks,  each  perforated  for  two  glass 
tubes.  These  corks  can  be  secured  from  the  dealer  who  sells 
you  the  flue-gas  apparatus.  Then,  fit  each  bottle  with  one  long 
glass  tube  and  one  short  one  in  the  manner  shown.  If  the  top 


FIG.  16. — Arrangement  for  collecting  a  time  gas  sample. 

of  each  glass  tube  is  heated  and  bent  over,  as  shown  at  a,  the 
rubber  tubing  is  not  so  likely  to  kink  up  and  stop  the  flow  of 
water. 

Fill  one  bottle  full  and  the  other  about  one-eighth  full  of 
water.  Connect  the  long  tube  of  each  bottle  with  a  length  of 
rubber  tubing  about  6  ft.  long;'  connect  each  short  tube  with  a 
length  of  rubber  tubing  about  12  to  1 8  in.  long  and  in  the  end 
of  these  short  lengths  insert  a  glass-tube  nipple,  4  to  6  in.  long 
as  shown. 

Arrange  the  bottles  one  above  the  other,  as  shown  in  Fig.  16, 
and  let  water  siphon  into  the  lower  bottle  until  it  is  full  and  water 


FUEL  ECONOMY  AND  CO2  RECORDERS 


begins  to  run  out  at  b.  Then,  set  pinch  cock  c  and  reverse  the 
bottles,  connecting  b  with  the  tubing  d.  Before  doing  this, 
however,  apply  the  small  hand  pump,  which  comes  with  the  flue- 


FIG.  17. — Arrangement  of  sampling  bottles  and  apparatus. 

gas  apparatus,  to  the  end  of  the  tubing  d  and  expel  all  the  air  in 
the  piping;  then,  set  a  pinch  cock  on  d  as  close  to  the  lower  end 
as  possible.     If  these  directions  are  followed  closely,  very  little 
or  no  air  will  get  into  the  system  to  make  the  sample  unfair. 
Now,  release  all  pinch  cocks  and  allow  the  water  to  siphon 


FLUE  GAS  ANALYSIS  71 

from  the  upper  to  the  lower  bottle.  This  causes  a  vacuum  in  the 
upper  bottle  which  draws  in  the  gas  from  the  boiler. 

By  heating  the  end  of  one  of  the  long  glass  tubes  and  drawing 
it  down  to  a  finer  opening,  a  longer  time  will  be  required  to  siphon 
the  water  over  and  hence  to  fill  the  upper  bottle  with  gas.  If, 
for  instance,  an  8-hr,  sample  is  desired,  a  little  experimenting  with 
the  size  of  opening  in  the  glass  tube  will  result  in  getting  the  time 
of  water  flow  about  correct.  Of  course,  as  it  is  not  necessary  to 
have  more  than  perhaps  a  quarter  of  a  bottle  full  of  gas,  the  length 
of  time  required  for  the  water  to  siphon  over  does  not  matter 
much,  provided  it  is  longer  than  the  length  of  the  test  desired. 

When  the  desired  gas  sample  has  been  drawn  into  the  upper 
bottle,  set  all  pinch  cocks  and  arrange  the  bottles,  as  shown  in 
Fig.  17,  the  one  full  of  water  slightly  higher  than  the  other.  With 
this  arrangement  the  gas  is  under  a  slight  pressure  and  if  the 
system  is  accidentally  opened,  gas  will  escape,  but  no  air  will 
leak  in  to  spoil  the  sample.  Connect  the  gas  bottle  with  the  flue- 
gas  apparatus,  as  shown,  and  proceed  with  the  analysis  as 
explained  in  previous  paragraphs. 

As  water  aborbs  CO2,  the  water  in  the  collecting  bottles 
should  be  saturated  with  gas  before  samples  for  testing  are  col- 
lected. This  can  be  done  by  drawing  some  gas  first  into  one 
bottle,  then  into  the  other  and  allowing  it  to  stand  for  some  time, 
shaking  the  bottles  now  and  then  to  induce  complete  saturation. 

CARE  OF  APPARATUS 

In  course  of  time  the  rubber  tubing  and  connections  used 
with  the  Orsat  will  become  hard  and  crack,  when  they  will  need 
renewing. 

The  caustic  will  affect  the  glass  pipettes.  Hence,  if  the 
apparatus  is  not  to  be  used  for  some  length  of  time,  it  is  well  to 
empty  the  apparatus  before  storing  it  away. 

The  glass  stop  cocks  must  be  kept  clean  or  they  will  not  remain 
air-tight.  Also,  if  they  are  not  lubricated  frequently,  they 
may  become  stuck  and  cause  trouble.  A  good  lubricant  to 
use  is  vaseline.  This  point  should  be  attended  to  frequently 
if  trouble  is  to  be  avoided. 


CHAPTER  IV 
HEAT  LOST  IN  FLUE  GASES 
HEAT  LOST  UP  THE  CHIMNEY 

When  a  pound  of  fuel  is  burned  under  a  boiler  its  available  heat 
is  distributed  in  a  number  of  ways.  The  largest  part  is  trans- 
ferred to  the  water  within  the  boiler  and  converts  some  of  it  into 
steam.  But  from  20  to  60  per  cent,  is  lost  in  various  ways. 
The  greatest  loss  is  due  to  the  heat  carried  up  the  chimney  by  the 
flue  gases,  and,  as  this  loss  depends  to  a  large  extent  upon  the  skill 
and  care  employed  in  operation,  it  is  one  in  which  every  engineer 
should  be  greatly  interested  and  about  which  he  should  be 
thoroughly  posted. 

If  after  a  pound  of  flue  gas  has  come  in  contact  with  the 
heating  surface  of  the  boiler  and  has  given  up  some  of  its  heat  to 
the  water  within,  it  passes  out  to  the  chimey  at,  say,  500  deg.  F., 
how  much  heat  is  lost  or  carried  up  the  chimney? 

All  the  heat  that  the  gas  contains,  over  and  above  what  the  air 
and  coal  from  which  it  was  formed  contained,  was  derived  from 
the  combustion  of  the  coal.  Then  to  all  intents  and  purposes  the 
heat  lost  with  every  pound  of  flue  gas,  expressed  in  B.t.u.,  must 
be  the  product  of  the  number  of  degrees  difference  in  temperature 
between  the  air  entering  the  furnace  and  the  flue  gas  going  out  of 
the  boiler,  multiplied  by  the  heat  required  to  raise  the  temperature 
of  a  pound  of  flue  gas  i  deg. 

SPECIFIC  HEAT 

This  brings  us  to  a  consideration  of  "  specific  heat,"  a  term  often 
employed  in  steam  engineering.  By  definition,  the  amount  of 
heat  required  to  raise  the  temperature  of  a  pound  of  water  i  deg. 

72 


HEAT  LOST  IN  FLUE  GASES  73 

is  one  B.t.u.  A  pound  of  air  requires  about  one-fourth  as  much 
heat  as  a  pound  of  water  for  a  rise  of  i  deg.,  and  a  pound  of  iron 
requires  only  about  one-eighth  as  much  as  water.  The  quantity 
of  heat  required  to  raise  the  temperature  of  a  given  amount  of 
substance  a  given  number  of  degrees  depends  upon  the  nature  of 
the  substance  and  is  different  in  almost  every  case.  Hence,  in 
problems  involving  quantity  of  heat  and  quantity  of  materials, 
it  is  often  important  to  know  the  amount  of  heat  required  to  cause 
a  rise  of  i  deg.  in  temperature  per  pound  of  material  under  con- 
sideration. This  quantity  is  called  the  specific  heat  of  the 
substance.  Thus,  the  specific  heat  of  iron  is  said  to  be  0.13,  be- 
cause a  pound  of  iron  requires  0.13  B.t.u.  to  raise  its  temperature 
i  deg. 

The  specific  heat  of  flue  gas  is  not  exactly  known,  nor  is  it 
uniform  for  all  temperatures.  That  is,  at  low  temperatures  it  is 
somewhat  less  than  at  high.  However,  the  most  commonly 
accepted  value  is  0.24,  and  hence  this  is  the  one  we  will  use. 

ESTIMATING  HEAT  LOST  IN  FLUE  GASES 

The  heat  lost  or  carried  up  the  chimney  by  the  flue  gases  per 
pound  of  fuel  burned  can  be  estimated  by  multiplying  the  weight 
of  the  gases  generated  per  pound  of  fuel  by  the  specific  heat  of  the 
gases  and  the  difference  in  temperature  between  the  gases  leaving 
the  boiler  and  the  air  entering  the  furnace.  The  answer  expresses 
the  loss  in  B.t.u.  This  calculation  can  be  written  as  a  formula, 
thus: 

L  =  0.24  W(T-  0, 
where 

L  =  B.t.u.  lost  up  chimney  per  pound  of  fuel  burned; 
0.24  =  specific  heat  of  the  flue  gases  (or  the  amount  of  heat 

required  to  raise  i  Ib.  of  the  gases  i  deg.); 
W  =  weight  of  flue  gases  formed  per  pound  of  fuel; 
T  =  temperature  of  gases  leaving  boiler,  degrees  F.; 
/  =  temperature  of  air  entering  furnace,  degrees  F. 


74  FUEL  ECONOMY  AND  CO2  RECORDERS 

WEIGHT  OF  GASES  PER  POUND  OF  FUEL 

To  make  the  foregoing  calculation  it  is  necessary  to  know  the 
weight  of  flue  gases  formed  per  pound  of  fuel  burned.  This  is 
found  by  the  following  formula,  which  looks  worse  than  it  really  is  : 


where 

W  =  weight  of  flue  gases  formed  per  pound  of  fuel  burned; 
3.032  =  a  constant; 

C  =  decimal  part  by  weight   of   carbon    (total  carbon) 

in  the  fuel  as  fired; 

N  =  percentage  by  volume  of  nitrogen  in  the  flue  gases; 
COz  =  percentage  by  volume  of  carbon  dioxide  in  the  flue 

gases; 
CO  =  percentage  by  volume   of  carbon  monoxide  in  the 

flue  gases; 
A  =  decimal  part  of  weight  of  ash  in  the  fuel  as  fired. 

The  proximate  coal  analysis  does  not  show  the  decimal  parts 
proportion  or  percentage,  of  total  carbon  in  the  fuel  ;  it  only  show, 
the  percentage  of  fixed  carbon.  Consequently,  in  order  to  use 
the  foregoing  formula,  we  will  have  to  estimate  or  guess  at  the 
amount  of  carbon  contained  in  the  volatile  matter,  add  this  to  the 
amount  of  fixed  carbon  and  consider  the  sum  as  being  the  amount 
of  total  carbon  in  the  fuel.  The  accompanying  chart,  Fig.  18,  de- 
veloped by  Professor  Marks  and  originally  published  in  POWER 
for  Jan.  14,  1913,  will  give  results  close  enough  for  our  purpose. 

ESTIMATING  TOTAL  CARBON  IN  COAL 

To  calculate  the  carbon  in  the  volatile,  add  together  the  per- 
centage of  fixed  carbon  and  volatile  matter  as  shown  by  the 
proximate  analysis  and  divide  this  sum  into  the  percentage  of 
volatile  matter.  The  quotient  multiplied  by  100  gives  the 
percentage  of  volatile  matter  in  the  combustible.  Having  found 


HEAT  LOST  IN  FLUE  GASES 


75 


this,  locate  a  corresponding  point  on  the  scale  at  the  bottom  of  the 
chart  and  trace  an  imaginaryJine  straight  up  to  the  curve  and  then 
horizontally  to  the  scale  at  the  left  margin  which  gives  the  per- 


s  Combustible,  Percent. 

•  ro  r\>  c 
•  O  ui  < 

y 

' 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

' 

/ 

/ 

/ 

/ 

/ 

Volatile  Carbon  in  th< 
*  o  < 

/ 

/ 

/ 

/ 

^/ 

/ 

> 

/ 

/ 

| 

°, 

/ 

J 

1 

)                           20                          30                         40                           50                        60 

Volatile     Matter  "in  the  Combustible,  Per  Cent. 
FIG.  1 8. — Chart  for  determining  the  carbon  in  the  volatile  matter. 

centage  of  volatile  carbon  in  the  combustible  matter.  Multiply 
the  percentage  thus  formed  by  the  percentage  of  combustible  in 
the  coal  and  divide  by  100  to  obtain  the  percentage  of  volatile 
carbon  in  the  coal.  Add  this  percentage  to  the  percentage  of 
fixed  carbon  in  the  coal  as  shown  by  the  proximate  analysis  to 
obtain  the  total  carbon  in  the  coal. 


76        FUEL  ECONOMY  AND  CO2  RECORDERS 

To  illustrate  with  a  numerical  example,  assume  that  we  wish 
to  estimate  the  percentage  of  total  carbon  in  a  coal  with  this 
analysis:  Moisture,  6.2  per  cent.;  volatile  matter,  16.8  per  cent.; 
fixed  carbon,  70.7  per  cent.;  ash,  6.3  per  cent.  The  sum  of  the 
percentage  of  fixed  carbon  and  volatile  matter  is 

70.7  +  16.8  =  87.5 

and  this,  divided  into  the  percentage  of  volatile  matter  and 
multiplied  by  100,  gives 

16.8 

X  ioo  =  19.2  per  cent. 


87-5 

volatile  matter  in  the  combustible. 

Locating  the  19.2  point  on  the  scale  at  the  foot  of  the  chart  and 
tracing  an  imaginary  line  straight  up  to  the  curve  and  over  to  the 
margin  we  get  8.2  as  the  percentage  of  volatile  carbon  in  the 
combustible.  And  this  multiplied  by  87.5,  the  percentage  of 
combustible  matter  in  the  coal,  and  divided  by  ioo,  gives 

8.2  X  87.5  -T-  ioo  =  7.2 

the  percentage  of  volatile  carbon  in  the  coal,  which  added  to  the 
percentage  of  fixed  carbon  in  the  coal  gives 

70.7  +  7.2  =  77.9 
the  percentage  of  total  carbon  in  the  coal. 

ESTIMATING  NITROGEN 

The  flue-gas  analysis  as  made  according  to  the  directions  given 
in  previous  chapters  gives  the  percentage  by  volume  of  carbon 
dioxide  (CO2),  oxygen  (O)  and  carbon  monoxide  (CO).  In 
addition  to  these  there  exists  water,  in  the  form  of  superheated 
steam,  nitrogen  and  sometimes  hydrogen  and  various  hydro- 
carbons. The  steam  condenses  and  only  a  little  of  it  gets  to 


HEAT  LOST  IN  FLUE  GASES  77 

the  flue-gas  apparatus.  All  the  other  constituents  except  the 
nitrogen  form  a  small  percentage  of  the  total  volume.  Partly 
because  of  this  fact  and  partly  because  it  is  difficult  to  detect  and 
measure  them,  they  are  usually  ignored  entirely.  Thus,  the  dif- 
ference between  100  and  the  sum  of  the  percentages  of  CC>2,  O 
and  CO  is  taken  as  the  percentage  of  nitrogen  (N)  contained  in 
the  flue  gas. 

To  illustrate,  if  the  flue-gas  analysis  shows  1 1  per  cent.  CO2,  8 
per  cent.  O  and  0.8  per  cent.  CO,  the  percentage  of  nitrogen  in  the 
flue  gas  would  be  taken  as 

100  -  (n  +  8  +  0.8)  =  80.2 

This  practice  is  followed  because  there  is  no  liquid  or  chemical 
solution  capable  of  combining  and  absorbing  nitrogen  like  CO2 
O  and  CO  are  combined  and  absorbed. 

With  equal  temperature  and  pressure  CO2  has  the  same  volume 
as  the  oxygen  required  for  its  combustion.  That  is,  if  it  requires 
30  cu.  ft.  of  pure  oxygen  at  a  certain  temperature  and  atmos- 
pheric pressure  to  completely  burn  a  pound  of  pure  carbon  the 
CO2  formed  will  have  a  volume  of  just  30  cu.  ft.  when  cooled  down 
to  the  temperature  at  which  the  oxygen  was  measured.  The  vol- 
ume of  carbon  monoxide  is  twice  that  of  the  oxygen  required  in 
its  formation.  Thus,  the  sum  of  the  percentage  of  CO2  and  O 
and  one-half  the  CO  should  always  equal  21  (the  percentage  by 
volume  of  oxygen  in  the  air)  when  carbon  alone  is  the  combustible. 
But  in  the  average  plant  carbon  is  rarely  the  only  combustible  in 
the  fuel;  it  is  almost  always  accompanied  by  hydrogen. 

When  hydrogen  burns  it  forms  steam  which  practically  all 
condenses  and  never  gets  to  the  flue-gas  apparatus.  Thus,  the 
hydrogen  sidetracks  the  oxygen  of  the  air  required  for  its  com- 
bustion but  leaves  the  nitrogen  to  pass  on  to  the  flue-gas  appa- 
ratus along  with  the  nitrogen  of  the  air  required  for  the  combus- 
tion of  the  carbon.  The  result  is  that  the  sum  of  the  three 
oxygen  constituents  of  the  flue  gas  (CO2,  O,  CO)  do  not  add  up  to 
21,  but  to  some  smaller  figure,  the  exact  value  of  which  depends, 


78  FUEL  ECONOMY  AND  CO2  RECORDERS 

of  course,  upon  the  quantity  of  available  hydrogen  contained  in 
the  fuel. 

Using  the  data  given  in  the  last  lesson  for  coal  and  flue-gas  an- 
alysis in  this  lesson,  the  formula  for  estimating  the  weight  of  flue 
gases  formed  per  pound  of  fuel  burned  works  out  thus 


w  =  3.032  x  0.779  jfqfg  +  (J  -  °-°63)  =  17  #• 

Assuming  that  the  temperature  of  the  gases  as  they  leave  the 
boiler  is  520  deg.  F.  and  that  the  temperature  of  the  air  entering 
the  furnace  is  70  deg.,  the  formula  for  calculating  the  heat  lost 
up  the  chimney  in  the  flue  gases  would  work  out  thus 

L  =  0.24  X  17  (520  —  70)  =  1836  B.t.u. 

If  the  coal  in  the  foregoing  illustration  had  a  heat  value  of, 
say,  13,200  B.t.u.  per  pound,  as  fired,  the  percentage  of  heat  lost 
with  the  flue  gases  would  be 

6 

X  ioo  =  13.9  per  cent. 


RATIO  OF  AIR  SUPPLIED  TO  AIR  REQUIRED 

It  is  often  desirable  to  know  what  the  ratio  is  between  the 
amount  of  air  actually  supplied  per  pound  of  coal  and  the  amount 
theoretically  required.  This  can  be  estimated  by  means  of  the 
following  simple  equation: 


#-(3.78X0) 

where  R  equals  the  ratio  of  the  air  supplied  per  pound  of  fuel  to 
the  amount  theoretically  required  and  N  and  O  equal  the  per- 
centage by  volume  of  the  nitrogen  and  oxygen,  respectively,  in 
the  flue  gases,  as  shown  by  the  analysis. 

Using  the  data  previously  given  the  ratio  would  be 

80.2 


80.2  -  (3.78  X  8) 


HEAT  LOST  IN  FLUE  GASES 


79 


This  means  that  for  every  pound  of  air  required  by  the  coal  1.6  Ib. 
was  supplied.     Hence,  the  percentage  of  excess  air  is 

-  X  ioo  =  60 


Ball- 


MEASURING  FLUE-GAS  TEMPERATURE 

Thermometers  with  a  range  up  to  212  or  a  little  higher  are 
cheap  enough  that  no  difficulty  need  stand  in  the  way  of  measuring 
the  temperature  of  the  air  entering  the  furnace;  that  is,  the  air  in 
the  boiler  room.  But  as  the  temperatures  to  be  measured  get 
beyond  500  deg.  F.,  which  is  often  the  case  with  flue  gases,  the 
cost  of  the  pyrometer  (the  name  used  for  high-range  thermom- 
eters) begins  to  be  an  important 
consideration.  In  some  plants  the 
expense  of  purchasing  a  standard 
form  of  pyrometer  may  not  be  war- 
ranted, in  others  it  may  be  impossi- 
ble to  show  the  management  the  ad-  • 
vantage  of  keeping  constant  records  Plastic 
on  the  flue-gas  temperature.  In 
such  cases  the  engineer  may  and 
should  for  his  own  benefit  provide 
himself  with  the  means  of  making 
an  occasional  observation  of  the  flue- 
gas  temperature.  This  he  can  do  at 
reasonably  moderate  cost. 

HOME-MADE  APPARATUS 


Pipe--- 


Sand 


Numerous  means  are  available 
but  only  one  will  be  presented  here. 
The  required  equipment  consists  of 
the  bomb  shown  in  Fig.  19  and  a 
chemical  thermometer  having  a 
range  of  1000  deg.  F.  The  latter 
may  be  procured  of  any  chemists'  glassware  supply  house  at 
a  cost  of  from  $5  to  $10. 


FIG.  19. — Sand  bomb  and 
thermometer  for  measuring 
flue-gas  temperature. 


8o        FUEL  ECONOMY  AND  CO2  RECORDERS 

The  bomb  consists  of  a  length  of  4-in.  pipe  capped  at  one  end 
and  a  length  of  J-in.  pipe  extending  through  the  center,  as 
shown,  to  serve  as  the  thermometer  well.  Sand  is  packed  in 
about  the  j-in.  pipe  and  held  in  place  by  means  of  a  layes  of 
plastic  asbestos  at  the  open  end.  The  length  of  the  piper  is 
determined  by  the  length  of  the  thermometer.  The  J-in.  pipe 
should  be  of  such  a  length  that  when  the  thermometer  is  inserted 
it  will  be  inclosed  as  high  as  the  4oo-deg.  point  on  the  scale.  The 
4-in.  pipe  should  be  6  in.  longer,  as  shown.  A  bail  of  wire  or 
thin,  narrow  flat  iron  attached  as  shown  completes  the  bomb. 

When  it  is  desired  to  take  the  temperature  of  the  flue  gases,  the 
bomb  (without  the  thermometer)  is  hung  in  the  middle  of  the 
path  of  the  flue  gases  as  near  to  the  point  at  which  they  leave  the 
boiler  as  conveniently  possible.  After  a  half  to  three-quarters  of 
an  hour  the  bomb  is  removed  and  the  thermometer  inserted  as 
quickly  as  possible.  In  a  few  seconds  the  thermometer  will  indi- 
cate the  temperature  of  the  sand  which  will  be  practically  the 
same  as  that  of  the  flue  gases. 


PRACTICE  PROBLEMS 

From  the  following  data  estimate  the  percentage  of  excess  air 
supplied  to  the  furnace,  the  number  of  B.t.u.  carried  up  the 
chimney  by  the  flue  gases  and  the  percentage  of  loss  based  on  the 
heat  value  of  the  coal. 

Proximate  analysis  of  coal,  moisture,  4.5  per  cent.;  volatile, 
18.6  per  cent.;  fixed  carbon,  65.2  per  cent.;  ash,  11.7  per  cent.; 
B.t.u.,  13,160.  Flue-gas  analysis,  CO2,  6.3  per  cent.;  O,  11.7 
per  cent.;  CO,  0.4  per  cent.  Temperature  of  air  in  boiler  room, 
75  deg.;  temperature  of  gases  leaving  boiler,  515  deg. 

If  the  above  coal  costs  $3.10  per  net  ton  (2000  Ib.)  and  if  under 
the  present  conditions  6200  tons  are  consumed  per  year  what 
would  be  the  yearly  saving  effected  if  the  average  percentage  of 
CC>2  were  raised  to  10.7  and  the  O  reduced  to  7.3,  other  conditions 
remaining  the  same? 


HEAT  LOST  IN  FLUE  GASES  8l 

SOLUTION  OF  PRACTICE  PROBLEMS 

The  percentage  of  excess  air  supplied  to  the  furnace  may  be 
determined  from  the  formula  for  calculating  the  ratio  of  air 
supplied  to  air  required,  which  is  as  follows: 


R  = 


N  -  (3.78  X  O) 


From  the  data  given,  N,  the  percentage  of  nitrogen  in  the  flue 
gas,  equals 

100  —  (6.3  +  1  1.  7  +  0.4)  =  81.6 


Substituting  in  the  formula  gives 

81.6 81.6 

~  81.6  -  (3.78  X  11.7)  ~  37-37 


=  2.18 


Thus,  2.18  Ib.  of  air  was  supplied  for  every  pound  theoretically 
required.  Hence,  the  amount  of  excess  air  supplied  with  each 
pound  required  is 

2.18  —  i  =  1.18/6. 

This  excess  amount  divided  by  the  required  amount  and  mul- 
tiplied by  100  gives 

— '- —  X  ioo  =  118  per  cent. 

excess  air  supplied  to  the  furnace. 

To  calculate  the  B.t.u.  carried  up  the  chimney  by  the  flue 
gases  per  pound  of  coal  burned  it  is  first  necessary  to  estimate 
the  weight  of  flue  gases  formed  per  pound  of  coal.  And  before 
this  quantity  can  be  estimated  it  is  necessary  to  estimate  the 
decimal  part  by  weight  of  total  carbon  in  the  fuel.  The  decimal 
part  of  fixed  carbon  is  given  (expressed  as  a  percentage)  in  the 
proximate  analysis  of  the  coal,  and  equals  0.652.  To  this  must 
be  added  the  decimal  part  of  volatile  carbon,  which  is  estimated 

6 


82  FUEL  ECONOMY  AND  CO2  RECORDERS 

in  the  manner  explained  by  means  of  the  chart  in  Fig.  18.  The 
sum  of  the  percentages  of  fixed  carbon  and  volatile  matter  is 
65.2  +  18.6  =  83.8,  and  this,  divided  into  the  percentage  of 
volatile  matter  and  multiplied  by  100,  gives 

18.6. 

£— -  X   100  =   22.2 
03.0 

the  percentage  of  volatile  matter  in  the  combustible. 

Locating  as  closely  as  possible  the  22.2  per  cent,  point  at 
the  bottom  of  the  chart,  and  tracing  an  imaginary  line  up  to  the 
curve  and  over  to  the  side  scale,  we  get  10.4,  the  percentage  of 
volatile  carbon  in  the  combustible.  And  this,  multiplied  by  the 
percentage  of  combustible  in  the  coal  (83.8)  and  divided  by  100, 
gives 

10.4  X  83.8  = 
100  *' 

the  percentage  of  volatile  carbon  in  the  coal.  Shifting  the 
decimal  point  two  places  to  the  left  reduces  this  percentage  to 
a  decimal  fraction.  Adding  this  fraction  to  0.652,  the  decimal 
part  of  fixed  carbon  in  the  coal,  gives 

0.652  +  0.087  =  °-739 

or  practically  0.74,  which  is  the  decimal  part  of  total  carbon  in 
the  coal. 

The  formula  for  estimating  the  weight  of  gases  formed  per 
pound  of  coal  burned  is 


Substituting,  gives 

W  --  3.032  X  0.74  (6  3  +  0  J  +  d  ~  0.117) 
W  =  2.24  (86I<6)  +  0.88  =  28.16  Ib. 

gases  formed  per  pound  of  coal  burned. 


HEAT  LOST  IN  FLUE  GASES  83 

The  B.t.u.  carried  up  the  chimney  per  pound  of  coal  burned  is 
estimated  by  this  formula. 

L  =  0.24  W  (T  -t) 
Substituting,  gives 

L  =  0.24  X  28.16  (515  -  75) 
L  =  6.76  X  440  =  2974  B.t.u. 

carried  up  the  chimney  by  the  flue  gases  per  pound  of  coal 
burned. 

The  percentage  of  loss  is  the  number  of  B.t.u.  carried  up  the 
chimney  per  pound  of  coal  divided  by  the  heat  value  of  the 
coal  and  multiplied  by  100,  thus 

,    X  ioo  =  22.6  per  cent,  loss 
13,160 

There  are  several  ways  in  which  the  answer  to  the  last  prob- 
lem can  be  obtained.  The  simplest,  although,  perhaps,  not  the 
shortest,  is  to  find  the  percentage  of  heat  loss  in  the  second  case 
and  subtract  this  loss  from  the  loss  we  have  already  worked  out 
for  the  first  case.  The  difference,  divided  by  the  heat  value 
of  the  coal,  will  represent  the  percentage  of  coal  saved  per  year. 
Then,  the  number  of  tons  thus  shown  to  be  saved,  multiplied  by 
the  cost  per  ton,  will  give  the  annual  saving  in  dollars  and  cents. 

First,  using  the  formula  for  the  weight  of  flue  gases  formed,  gives 

W  -  3.032  X  °-74(10-7!j_0J  +  (i  -  0.117) 
+  0.88  =  17.34  Ib. 


the  weight  of  flue  gases  formed  per  pound  of  coal. 

Next,  substituting  this  value  in  the  formula  for  estimating 
the  heat  lost  up  the  chimney,  gives 

L  =  0.24  X  17-34  (5i5  -  75) 
L  =  4.16  X  440  =  1830  B.t.u. 

carried  up  the  chimney  by  the  flue  gases  per  pound  of  coal. 


84  FUEL  ECONOMY  AND  CO2  RECORDERS 

In  the  first  case,  2974  B.t.u.  was  lost  up  the  chimney  per  pound 
of  coal.    Hence  the  saving  is 

2974  —  1830  =  1144  B.t.u. 
per  pound  of  coal.     In  percentage  this  saving  amounts  to 

TT  A  A 


X  ioo  =  8.69  per  cent. 


As  8.69  per  cent,  of  each  pound  of  coal  is  saved,  8.69  per  cent. 
of  each  ton  and  hence  8.69  per  cent,  of  all  the  coal  is  saved. 
Thus,  the  saving  in  tons  per  year  equals 

9  =  538-78 
and  the  saving  in  dollars  and  cents  equals 

538.78  X  3-10  =  $1670.22 

Loss  DUE  TO  INCOMPLETE  COMBUSTION 

In  one  of  the  early  Chapters  we  learned  that  carbon  under 
certain  conditions  will  only  partially  burn,  forming  carbon 
monoxide  (CO)  instead  of  carbon  dioxide  (CO2)  and  creating 
only  4450  B.t.u.  per  Ib.  of  carbon  instead  of  14,600.  Hence,  for 
every  pound  of  carbon  only  partially  burned 

14,600  —  4450  =  10,150  B.t.u. 
is  lost. 

If  the  flue-gas  analysis  shows  that  CO  exists  it  may  be  im- 
portant or  desirable  to  know  the  amount  of  heat  loss  due  to 
incomplete  combustion.  The  following  formula  is  convenient  for 
estimating  this  quantity. 

L>  =  IO'I5°  (co^co)  c 

Where 

L'  =  B.t.u.  lost  per  pound  of  fuel; 


HEAT  LOST  IN  FLUE  GASES  85 

CO  =  Percentage  by  volume  of  carbon  monoxide  in  the  flue 

gas; 
C02  =  Percentage  by  volume  of  carbon  dioxide  in  the  flue 

gas; 
C  =  Decimal  part  by  weight  of  total  carbon  in  the  fuel. 

To  illustrate,  assume  the  following:  CO,  1.3  per  cent.;  CO2, 
15.2  per  cent.,  and  total  carbon  in  the  fuel,  72.8  per  cent.  The 
heat  loss  due  to  incomplete  combustion  would  be,  in  such  a  case, 


L'  =  10,150  (--^-  -  )  0.728 
\i.3  +  15.27 

L'  =  10,150  X  4r     X  0.728  =  582.27  B.t.u.  per  Ib. 


CHAPTER  V 
DRAFT  AND  ITS  MEASUREMENT 

In  a  natural-draft  plant  the  chimney  plays  a  far  larger  part 
than  is  commonly  suspected  in  determining  whether  operating 
results  are  to  be  satisfactory  or  not.  A  chimney  which  is  too 
small  means  poor  draft  and  sluggish  combustion  with  all  its 
attending  annoyances  and  losses.  A  chimney  which  is  too  large 
means  waste  of  money  in  first  cost  and,  often,  loss  due  to  excess 
air.  Consequently,  it  is  fitting  that  a  few  points  about  chimney 
design  be  taken  up  at  this  juncture. 

NATURAL  DRAFT 

Before  the  actual  formulas  for  figuring  chimney  sizes  suitable 
for  certain  conditions  are  studied,  it  is  well  to  get  a  thorough 
understanding  of  the  principles  of  natural  draft. 

This  old  earth  is  entirely  surrounded  by  an  ocean  of  a  gas 
mixture  called  air.  The  depth  of  this  ocean  is  not  known,  but 
is  estimated  at  all  the  way  from  50  to  500  miles.  As  we  transact 
most  of  our  business  at  the  bottom  of  this  ocean  we  do  so  under 
a  normal  pressure,  due  to  the  weight  of  the  ah*,  of  14.7  Ib.  per  sq. 
in.  at  sea  level.  As  we  get  above  sea  level,  naturally  the  pres- 
sure decreases  because  there  is  less  air  above  pressing  down. 

The  volume  of  all  gases,  air  included,  is  greatly  influenced 
by  change  in  temperature  or  pressure.  With  increase  in 
temperature  the  air  expands,  that  is,  the  volume  increases. 
With  increase  in  pressure  the  volume  diminishes.  These  changes 
in  volume,  due  to  changes  in  temperature  or  pressure  or  both, 
take  place  according  to  well  known  laws.  Hence,  if  the  volume 
of  given  weight  of  a  gas  at  a  given  temperature  and  pressure  is 
known,  it  is  possible  to  figure  exactly  what  the  volume  would  be 
at  some  other  temperature  and  pressure. 

86 


DRAFT  AND  ITS  MEASUREMENT  87 

For  every  ordinary  purpose  we  may  take  the  atmospheric 
pressure  (at  or  near  sea  level)  as  14.7  Ib.  per  sq.  in.,  although 
actually  the  pressure  is  constantly  varying  slightly,  due  to 
changes  in  the  condition  of  the  air.  As  natural  draft  has  to  do 
with  ah*  at  atmospheric  pressure  only,  and  as  we  have  decided  to 
consider  this  pressure  as  being  fixed  at  14.7  Ib.  per  sq.  in.,  there 
remains  only  one  variable  —  temperature  —  to  consider  during 
the  study  of  the  present  subject. 

ABSOLUTE  TEMPERATURE 
With  the  pressure  remaining  the  same  the  volume  of  a  given 

weight  of  air  increases  or  decreases  —  of  its  volume  at  32  deg. 

492 

F.  for  every  increase  or  decrease  of  i  deg.  in  its  temperature. 
For  instance,  if  a  pound  of  air  at  atmospheric  pressure  and  32 
deg.  F.  has  a  volume  of  12.39  cu.  ft.,  at  100  deg.  F.  (the  pressure 
remaining  the  same)  its  volume  will  have  increased  by 


I2'39  X 
Hence,  its  volume  at  100  deg.  would  be 

12.39  +  1.71  =  14.1  cu.  ft. 

This  law  holds  good  for  all  temperatures  dealt  with  in  steam 
power-plant  work.     If  it  held  good  for  all  possible  temperatures, 

that  is,  if  a  gas  continued  to  shrink  --  of  its  volume  at  32  deg. 

F.  for  every  degree  drop  in  temperature,  when  the  temperature 
dropped  the  32  deg.  from  the  freezing  point  to  zero  and  then 
dropped  460  deg.  below  zero,  thus  dropping  a  total  of 

460  +  32  =492  deg. 

the  gas  would  disappear  entirely.  Such  low  temperature  has 
never  actually  been  attained;  hence,  we  do  not  know  whether 


88        FUEL  ECONOMY  AND  CO2  RECORDERS 

or  not  a  change  in  the  law  takes  place,  but  it  is  quite  certain 
that  one  does. 

As  a  result  of  the  above  law  governing  the  expansion  and 
contraction  of  gases  through  change  in  temperature  an  imaginary 
standard  for  temperature  has  been  invented,  which  is  convenient 
to  use  when  solving  problems  dealing  with  gas  temperature  and 
volume.  Temperatures  expressed  according  to  this  standard  are 
known  as  absolute  temperatures.  The  zero  according  to  the 
absolute  scale  is  460  deg.  below  the  zero  on  the  Fahrenheit  scale. 
Hence,  the  absolute  temperature  of  any  gas  is  its  Fahrenheit 
temperature  plus  460. 

For  instance,  the  absolute  temperature  of  a  gas  at  92  deg.  F.  is 

92  +  460  =  552  deg. 

The  convenient  thing  about  these  absolute  temperature  units 
is  the  fact  that  where  the  pressure  remains  the  same  the  volume 
varies  in  direct  proportion  to  the  absolute  temperature. 

To  illustrate,  if  the  volume  of  a  gas  is  14  cu.  ft.  per  Ib.  at  one 
temperature,  say,  60  deg.,  and  it  is  desired  to  estimate  the 
volume  at  some  other  temperature,  say,  109  deg.,  the  pressure 
being  the  same  in  each  case,  it  is  simply  necessary  to  multiply 
by  the  ratio  (expressed  as  a  common  fraction)  of  the  two  absolute 
temperatures.  The  absolute  temperature  corresponding  to  60 
deg.  F.  is  60  +  460  =  520  deg.,  and  that  corresponding  with 
109  deg.  is  109  -f-  460  =  569  deg.  Hence,  the  volume  at  109 
deg.  would  be 

15-31™.  A 


The  following  simple  formula  gives  the  pressure,  volume  or 
temperature  of  one  pound  of  air  when  any  two  of  these  factors 
are  known 

Pv  =  53-37  T 
where 

P  =  absolute  pressure  in  pounds  per  square  foot; 
v  =  volume  in  cubic  feet  of  i  Ib.  of  air; 
T  =  absolute  temperature  of  the  air  in  degrees  Fahrenheit. 


DRAFT  AND  ITS  MEASUREMENT  89 

Transposed  to  the  form  most  convenient  for  calculating 
volume  the  formula  is  written  thus 

53-37  T 
~^~ 

To  apply  in  a  practical  problem,  assume  it  is  desired  to  figure 
the  volume  of  a  pound  of  air  at  atmospheric  pressure  (14.7  Ib. 
per  sq.  in.)  and  70  deg.  F.  The  absolute  temperature  correspond- 
ing with  70  deg.  F.  is  70  +  460  =  530  deg.  The  pressure  per 
square  foot  in  the  present  example  is  14.7  X  144  =  2116.8  Ib. 
Then,  substituting  these  values  in  the  formula,  we  have 


MEASUREMENT  OF  DRAFT 

Draft,  whether  mechanical  or  natural,  is  measured  by  a  draft 
gage  and  usually  expressed  in  inches  of  water  similarly  to  a 
vacuum,  except  the  latter  is  expressed  in  inches  of  mercury. 

The  simplest  form  of  draft  gage  is  a  U-shaped  tube  of  ordinary 
glass,  as  in  Fig.  20,  and  is  usually  fitted  with  a  scale  in  inches  and 
decimal  fractions  of  an  inch.  One  leg  of  the  tube  is  connected 
with  the  furnace,  flue,  chimney,  or  other  place  where  the  draft  is 
to  be  measured,  and  the  other  leg  is  left  open  to  the  atmosphere. 
The  draft  is  the  inches  of  difference  in  level  between  the  water  in 
the  two  legs  as  indicated  in  the  figure. 

There  are  numerous  other  forms  of  gage,  most  of  which  are 
designed  to  give  more  accurate  readings  for  small  variations  in 
draft  than  the  one  shown,  but  the  principle  of  construction  and 
the  unit  of  measurement  are  the  same. 

PRINCIPLE  OF  DRAFT 

Probably  every  reader  understands  the  underlying  principle  of 
natural  draft  in  a  general  way,  but  some  may  be  a  little  confused 
as  to  how  the  height  of  chimney  and  temperature  of  gases  affect 


FUEL  ECONOMY  AND  CO2  RECORDERS 


intensity  of  draft.     So,  to  make  this  basic  theory  quite  evident 
to  all,  a  little  space  will  be  given  it  at  this  point. 

Imagine  a  pair  of  frictionless  and  sensitive  plunger  scales,  as 
in  Fig.  22,  located  in  an  absolute  vacuum.  The  connecting 
tube  A  is  filled  with  some  frictionless  and  weightless  fluid.  Next, 
imagine  that  1000  cu.  ft.  of  air  at  some  ordinary  atmospheric 
pressure  and  temperature,  say,  14.7  Ib.  per  sq.  in.  and  68  deg.  F., 
were  wrapped  up  in  a  bundle  and  placed  on  the  platform  of  one 
plunger  and  1000  cu.  ft.  of  air  at  the  same  pressure  but  at  a  tern- 


ToChimney 

Rubber  Tube 
gOpen 


Water-- 


r 


FIG.  20 


Level  J-- 


ievet  F, 


6 

Aired-  14  7lb. 
pressure  and 
GdPeg.F 

Air  at  14  7lb. 
pressure  and 
WODeq.F     -' 

H 

\[ 

/ 

Level? 


1000 
Cu.H-.of 
A/raf 
600  Deq 
Weighf 
37%  Lb. 


FIG.  21 

FIGS.  20,  21  and  22. 


FIG.  22 


perature  of  600  deg.  F.  were  done  into  a  similar  bundle  and 
placed  on  the  other  plunger  platform. 

The  weight  of  the  68-deg.  air  would  be  75  Ib.  while  that  of  the 
6oo-deg.  air  would  be  37.5  Ib.  or  just  one-half  that  of  the  former. 
The  cooler  air  being  37.5  Ib.  heavier  than  the  warmer,  if  the  pin 
B  were  withdrawn,  plunger  C  would  tend  to  sink  and  plunger  D 
to  rise,  due  to  the  37.5  Ib.  difference. 

Now,  assume  that  the  plungers  C  and  D  are  removed,  as  in 


DRAFT  AND  ITS  MEASUREMENT  91 

Fig.  21,  and  that  leg  G  is  filled  down  to  the  level  F  with  1000  cu. 
ft.  of  air  at  14.7  Ib.  pressure  and  68  deg.  F.  and  leg  H  to  the  same 
level  with  air  at  the  same  pressure  but  at  a  temperature  of  600 
deg.,  the  top  of  both  legs  being  open. 

If  each  leg  is  100  ft.  high  above  level  F,  the  inside  area  of  each 
must  be  10  sq.  ft.  or  1440  sq.  in.,  and  the  pressure  per  square  inch 
at  level  F  in  leg  G,  due  to  the  weight  of  air  in  the  leg,  must  be  75 
(weight  of  1000  cu.  ft.  of  air  at  14.7  Ib.  pressure  and  68  deg.), 
divided  by  1440;  which  equals  0.052  Ib.  per  sq.  in.* 

Similarly,  the  pressure  at  F  in  tube  H,  due  to  the  weight  of  the 
air  at  600  deg.,  must  be 

37.5  -r-  1440  =  0.026  Ib.  per  sq.  in. 

Thus,  there  is  a  difference  in  pressure  in  the  two  legs  at  level  F  of 
0.052  —  0.026  =  0.026  Ib.  per  sq.  in. 

with  a  consequent  tendency  of  the  air  in  leg  G  to  flow  into  leg  H 
and  push  out  the  lighter  air  in  the  latter. 

Now,  if  the  vacuum  be  destroyed  and  the  tube  be  submitted 
to  the  ordinary  atmospheric  pressure  (say,  14.7  Ib.  per  sq.  in.  at 
level  7)  the  tendency  of  the  cold  air  in  leg  G  to  force  out  the  hot 
air  in  H  will  be  just  as  strong  as  it  was  in  the  vacuum.  This  is 
true  because  the  pressure  at  level  F  in  leg  G  is  14.7  Ib.  per  sq.in. 
(the  atmospheric  pressure  at  level  /)  plus  the  weight  of  the  air 
contained  in  the  leg,  divided  by  the  square  inches  of  area  of  the 
tube,  thus 

J4-7  +  77—  =  I4.752  H>-  Per  sq.  in. 
1440 

*  This  method  of  calculating  the  pressure  due  to  the  weight  of  a  fluid 
is  used  simply  to  make  the  description  more  clear.  If  the  legs  were  not 
absolutely  uniform  in  sectional  area  throughout  their  height  this  method 
would  cause  error.  It  should  be  remembered  that  the  pressure  due  to  the 
weight  of  a  liquid  or  a  gas  depends  only  upon  the  vertical  depth  from 
the  surface  of  the  fluid  to  the  point  under  consideration  and  the  weight 
of  a  unit  volume  of  the  fluid.  The  size  and  shape  of  the  containing 
vessel  have  nothing  to  do  with  the  pressure. 


92  FUEL  ECONOMY  AND  CO2  RECORDERS 

Similarly,  the  pressure  at  level  F  in  tube  H  is 

37  5 
14-7  +  ~—  =  I4-726  #•  /*?r  *g.  *'». 

Hence,  the  tendency  of  the  cold  air  in  G  to  push  out  the  hot  air 
in  H  is  the  same  as  under  the  former  conditions,  the  difference  in 
pressure  being  the  same 

14.752  —  14.726  =  0.026  Ib.  per  sq.  in. 

Now,  as  the  pressure  and  temperature  of  the  air  outside  the 
tube  are  identical  with  those  of  the  air  within  leg  G,  this  leg 
performs  no  useful  function  and  may  be  dispensed  with,  when  we 
have  left  a  natural-draft  chimney. 

Thus,  we  see  that  natural  draft  is  due  to  a  difference  in  pressure 
due  to  a  difference  in  weight  between  two  columns  of  gas  of  equal 
height.  And  as  the  outside  pressure  (the  atmospheric  pressure) 
acting  on  these  two  columns  is  equal  for  any  given  height,  this 
difference  in  weight  depends  upon  the  difference  in  temperature. 
As  the  pressure  due  to  the  weight  of  a  column  of  fluid  depends 
only  upon  the  height  of  the  column  and  the  weight  of  a  unit 
volume  of  fluid,  and  not  upon  the  cross-sectional  area  nor  the 
shape  of  the  column,  the  intensity  of  draft  is  proportional  to  the 
height  of  the  chimney  above  the  fire. 

To  sum  up,  then,  the  intensity  of  draft  depends  upon  the 
height  of  the  chimney  and  the  difference  in  temperature  between 
the  outside  and  the  stack  gases. 

The  following  formula  may  be  used  to  estimate  the  intensity 
of  draft  to  be  expected  from  a  chimney  under  given  conditions. 

D  =  0.52  HX 
where 

D  =  draft  in  inches  of  water; 

H  =  height  of  chimney  above  grates  in  feet; 

P   —  atmospheric  pressure  in  pounds  per  square  inch; 

T   =  absolute  temperature  of  the  outside  air  in  degrees; 

T'  =  absolute  temperature  of  chimney  gases  in  degrees. 


DRAFT  AND  ITS  MEASUREMENT  93 

Thus,  with  a  chimney  175  ft.  high  above  the  grates  in  which 
the  gases  are  rising  at  a  temperature  of  560  deg.  F.  when  the 
outside  air  is  at  60  deg.  and  the  atmospheric  pressure  at  14.7 
Ib.  per  sq.  in.,  the  draft  would  be 

/>.  aS8  X  175  X  14-7 


D  =  0.52  X  175  X  14-7  X  0.00094  =  1.26  in. 


CHAPTER  VI 
CHIMNEY  DESIGN 

When  water  is  conveyed  in  a  pipe  the  quantity  delivered  per 
unit  of  time  depends  upon  the  diameter  and  length  of  the  pipe, 
the  friction  due  to  the  nature  of  the  pipe  surface  and  the  kind 
and  number  of  the  turns  in  the  pipe,  the  difference  between  the 
pressure  or  head  at  the  starting  point  and  at  the  delivery  point. 

For  illustration,  consider  a  i-in.  pipe  line,  300  ft.  long,  ar- 
ranged as  shown  in  Fig.  23.  Assume  that  under  the  conditions 
shown,  9  gal.  of  water  is  delivered  per  minute  and  that  it  is  de- 
sired to  increase  the  quantity  to,  say,  12  gal.  per  min.  As  the 
nature  of  the  pipe  surface  and  the  number  of  turns  cannot  be 
changed,  it  will  be  necessary  to  increase  the  head  H  or  increase 
the  diameter  of  the  pipe  to  secure  the  desired  result. 

The  increase  in  head  would  have  to  be  considerable,  something 
like  200  ft,  while  the  necessary  increase  in  diameter  would  be  but 
slight.  But,  if  it  were  required  to  deliver  the  original  quantity 
of  water  against  a  resistance  or  back  pressure  due  to,  say,  a 
partial  obstruction  at  the  end  E,  or  at  any  other  place,  increasing 
the  diameter  of  the  pipe  would  be  of  but  slight  use.  The  only 
benefit  derived  would  be  a  certain  reduction  in  the  friction  of 
the  pipe  itself,  which  would  leave  just  that  much  more  pressure 
available  at  E  for  overcoming  the  resistance  there,  resulting  in  a 
somewhat  increased  flow. 

On  the  other  hand,  any  increase  in  head  H,  produced  by 
raising  the  upper  tank,  would  almost  all  be  available  for  over- 
coming the  local  resistance  or  back  pressure  at  E,  the  only  amount 
lost  being  due  to  the  slight  additional  friction  of  the  required 
additional  length  of  vertical  pipe. 

The  principles  of  boiler-furnace  draft,  produced  by  a  chimney, 
are  very  similar  to  those  involved  in  the  foregoing  illustration. 
One  difference  in  actual  application  is  that  the  chimney  system 

94 


CHIMNEY  DESIGN 


95 


seemingly  works  upside  down.  The  boiler  room  itself  corresponds 
to  the  overhead  tank  in  Fig,  23;  the  furnace,  gas  passages  of  the 
boiler,  breeching  and  chimney  are  the  piping  system.  But, 
instead  of  the  flow  being  downward,  as  in  the  case  of  the  water 
system,  it  is  upward.  Nevertheless, 
gravity  is  the  actuating  force  in  both 
cases.  The  heavy  cool  air  outside 
the  chimney  containing  the  light,  hot 
gases  has,  due  to  the  force  of  gravity, 
a  continual  tendency  to  seek  its  own 
levels  in  the  chimney  and  force  up  the 
light  gases.  It  never  succeeds,  how- 
ever, for  as  long  as  the  fire  is  main- 
tained the  heavy  cool  air  is  converted 
into  light  hot  gas  in  passing  through 
the  fuel  bed. 

The  important  point  of  comparison 

b  e  twe  en 
the  water 
system  here 
illustra  ted 
and  a  nat- 
ural-draft 


-  - ZOO 


FIG.  23. — Illustration  to  show  principal  of  chimney  draft. 


system  is  that  similar  changes  in  dimensions  or  design  produce 
similar  results.  If  it  is  desired  to  increase  the  head  (or  draft) 
so  that  a  certain  rate  of  flow  may  be  maintained  against  a  given 
resistance,  logically,  the  height  of  the  water  pipe  or  chimney,  as 
the  case  may  be,  must  be  increased.  While  increasing  the  area 
of  the  piping  or  the  gas  passages  helps  to  a  slight  extent,  the 
main  resistance  (at  E,  Fig.  23,  or  at  the  fuel  bed  in  the  case  of 
a  draft  problem)  is  usually  so  large  that  only  a  change  in  height 
will  suffice.  In  other  words,  the  head  or  draft,  or  tendency  to 
flow  —  whichever  you  call  it  —  must  be  great  enough  so  that  the 
resistance  or  friction  will  be  overcome  and  there  will  still  re- 
main a  certain  amount  of  draft  to  produce  a  flow  or  velocity 
sufficient  to  handle  the  required  quantity  of  gas  per  unit  of  tune. 


96        FUEL  ECONOMY  AND  CO2  RECORDERS 

When  this  condition  has  been  fulfilled  the  size  of  breeching 
and  diameter  of  chimney  must  be  determined.  Here,  just  as 
with  the  water  piping,  the  area  of  the  passages  is  the  factor  which 
has  the  greatest  effect  on  the  capacity  (volume  of  gas  handled  per 
unit  of  time).  And  it  is  poor  economy  to  add  to  the  height  simply 
to  increase  the  capacity  by  making  the  velocity  abnormally  high. 

ESTIMATING  DRAFT  REQUIRED 

Before  we  are  in  a  position  to  design  a  suitable  chimney  for 
a  given  plant  we  must  have  some  data  as  to  the  draft  that  will 
be  required  under  the  working  conditions.  Knowing  this,  we 
can  then  determine  the  necessary  height.  To  estimate  the 
draft  that  will  be  required  we  must  know  the  approximate  nature 
of  the  fuel  to  be  burned,  the  rate  at  which  the  fuel  is  to  be  burned, 
the  grate  area,  the  type  of  boiler  to  be  used,  manner  of  baffling, 
length  of  the  breeching,  its  cross-sectional  area  and  the  number 
of  turns  it  makes.  In  fact,  we  should  know,  if  possible,  all  the 
factors  that  affect  the  draft  and  the  amount  of  their  influence. 

Unfortunately,  it  is  almost  impossible  to  permanently  deter- 
mine all  the  factors.  After  a  plant  has  been  running  a  year  or  so, 
it  may  be  necessary  to  change  the  grade  of  coal  used.  Or,  it 
may  be  necessary  to  add  more  boilers  than  were  originally  pro- 
vided for  or  to  greatly  overload  the  existing  plant.  All  these 
changes  would  have  their  effect  on  the  draft  requirements. 
Hence,  as  the  load  on  the  stack  is  usually  increased  and  but  seldom 
diminished,  it  is  a  good  and  safe  mistake  to  make  the  chimney 
too  large  rather  than  too  small.  The  intelligent  engineer  will 
offset  too  much  stack  capacity  by  a  careful  use  of  the  dampers, 
but  he  is  helpless  if  he  is  afflicted  with  a  heavily  overloaded 
chimney. 

The  study  of  draft  losses  in  a  boiler  installation  is  such  a 
broad  one  and  so  many  factors  enter  into  the  problems  involved 
that  it  is  impossible  to  do  more  than  briefly  outline  the  details 
here. 

In  calculating  the  draft  required  for  a  given  installation  allow 
o.ooi  in.  of  water  for  each  foot  in  the  length  of  the  breeching, 


CHIMNEY  DESIGN  97 

measured  from  the  chimney  to  the  nearest  boiler;  0.05  in.  for 
each  right-angle  turn  in  the  breeching,  and  0.4  in.  for  the  boiler 
or  boilers,  themselves. 

These  figures  are  based  on  average  conditions  and  they  are 
safe  for  use  with  most  of  the  ordinary  installations  where  the 
cross-sectional  area  of  the  breeching  is  20  per  cent,  greater  than 
the  smallest  free  cross-sectional  area  of  the  chimney  and  where 
the  boiler  is  of  any  standard  design  and  has  the  usual  baffle 
and  gas-passage  arrangements. 

After  having  allowed  a  certain  quantity  of  draft  for  overcoming 
the  resistance  of  the  boilers  and  gas  passages  it  is  next  necessary 
to  estimate  the  draft  required  at  the  fuel  bed.  This  factor  de- 
pends on  the  kind  and  size  of  the  fuel  to  be  burned  and  the  rate 
of  combustion  required  to  carry  the  load  on  the  boiler. 

To  estimate  the  rate  of  combustion  it  is  necessary  to  take  into 
consideration  the  maximum  horsepower  to  be  developed;  the 
pounds  of  coal  required  to  develop  one  horsepower-hour,  and  the 
area  of  the  grade.  Multiplying  the  first  two  factors  together  and 
dividing  by  the  last  gives  the  rate  of  combustion  in  pounds  per 
square  foot  of  grate  per  hour.  When  this  quantity  has  been 
estimated  the  approximate  draft  required  may  be  obtained  from 
Table  2,  compiled  from  some  data  given  in  "Stirling"  and  some 
furnished  by  the  Green  Engineering  Co. 

TABLE  2.— DRAFT  REQUIRED  IN  INCHES  OF  WATER  FOR 
VARIOUS  COALS  AND  RATES  OF  COMBUSTION 

Kind  of  Coal  Pounds  of  Coal  Burned  per  Sq.  Ft.  of  Grate  per  Hr. 

10       15       20       25       30      35       40      45       50 
Run-of-mine — bituminous 0.07  0.12  0.18  0.23  0.30  0.37  0.45  0.52  0.60 

Bituminous  slack 0.09  0.14  0.23  0.30  0.40  0.48  0.57  0.65  0.75 

Run-of-mine — semi-bitu- 
minous  0.07  0.14  0.23  0.32  0.45  0.60  0.77  0.95  1.2° 

Semi-bituminous  slack.. .  .0.1  o  0.16  0.28  0.40  0.57  0.73  0.90  i.io  1.37 

Anthracite  pea 0.16  0.30  0.45  0.64  0.88  1.25 

Anthracite   No.    i    buck- 
wheat  0.23  0.43  0.68  i.oo  1.40 

Anthracite    No.    3    buck- 
wheat  0.39  0.75  1.25  2.00 

7 


98        FUEL  ECONOMY  AND  CO2  RECORDERS 

To  illustrate,  assume  that  it  is  desired  to  find  the  draft  required 
by  an  installation  of  four  4oo-hp.  boilers,  the  maximum  load  on 
which  is  to  be  2000  hp.;  the  fuel  is  to  be  a  fair  grade  of  semi- 
bituminous  mine  run,  3^  Ib.  of  which  are  sufficient  to  develop 
one  boiler  horsepower  under  fair,  average  conditions;  the  area  of 
the  grate  under  each  boiler  is  88  sq.  ft.  The  breeching  is  30  ft. 
long  and  has  one  right-angle  turn. 

The  draft  loss  for  the  breeching  will  be 

(30  X  o.ooi)  -f-  0.05  =  0.08  in.  of  water 

and  assuming  0.4  in.  for  the  boilers  themselves,  the  total  draft 
loss  from  furnace  to  stack  will  be 

0.4  -f  0.08  =  0.48  in. 

As  2000  hp.  are  to  be  developed  requiring  the  combustion  of  3  J 
Ib.  of  coal  per  boiler  horsepower  per  hour,  the  total  coal  to  be 
burned  per  hour  equals 

2000  X  3.5  =  7000  Ib. 
As  the  total  grate  area  is 

4  X88  =  352^.  //., 

the  pounds  of  coal  burned  per  square  foot  of  grate  per  hour  will  be 

7000 

—  =    IQ.Q 
352 

By  referring  to  Table  2  it  will  be  found  that  0.23  in.  of  draft 
is  required  for  the  combustion  of  run-of-mine  semi-bituminous 
coal  at  a  rate  of  approximately  20  Ib.  per  sq.  ft.  of  grate  per 
hour.  Then,  adding  this  quantity  to  the  quantity  estimated 
to  be  required  to  overcome  the  resistance  of  the  boiler  and  breech- 
ing, we  have  a  total  draft  requirement  of 

0.48  +  0.23  =  0.71  in.  of  water. 


CHIMNEY  DESIGN  99 

The  next  step  is  to  estimate  the  height  of  chimney  required 
to  develop  this  amount  or  intensity  of  draft. 


HEIGHT  OF  CHIMNEY 

In  a  previous  chapter  a  formula  was  given  for  estimating  the 
amount  of  draft  to  be  expected  of  a  chimney  of  a  given  height 
under  certain  conditions.  By  rearranging  and  modifying  this 
formula  slightly  it  will  serve  for  estimating  the  height  of  chimney 
required  when  the  draft  is  known.  The  original  form  was 


By  transposing  the  factor  H  to  the  left  side  of  the  equation 
the  formula  takes  a  more  convenient  form  for  its  present  ap- 
plication, thus, 

H--    -D 


0.52  P- 


where  D  represents  the  draft  required  and  all  the  other  symbols 
are  the  same  as  in  the  previous  case. 

Now,  the  chimney  itself  offers  some  resistance  to  the  flow  of 
the  gases  and  allowance  should  be  made  for  this.  A  common 
estimate  of  this  loss  is  20  per  cent,  of  the  total  draft  developed. 
That  is,  if  a  perfectly  frictionless  imaginary  chimney  could 
develop,  say,  1.25  in.  of  draft,  in  actual  practice  a  chimney  of  the 
same  size  would  develop  only  80  per  cent,  of  this  figure,  or  i  in., 
the  other  20  per  cent,  being  lost  in  overcoming  the  friction  that 
every  actual  chimney  possesses. 

Hence,  in  applying  the  foregoing  formula  we  should  first 
increase  by  25  per  cent,  the  figure  representing  the  draft  required, 
so  as  to  obtain  a  chimney  of  such  height  that  20  per  cent,  of  the 
estimated  draft  may  be  lost  and  still  leave  the  required  amount. 


100  FUEL  ECONOMY  AND  CO2  RECORDERS 

Or,  better  still,  we  can  change  the  formula  to  take  care  of  this  by 
multiplying  the  draft  required  by  the  factor  1.25,  making  the 
formula  read  thus: 

n- ^D- 


0.52  P-, 


In  applying  this  formula  to  the  draft  problem  just  illustrated, 
we  must  first  ascertain  what  the  average  atmospheric  pressure 
(P)  is  at  the  location  of  the  plant.  At  or  near  sea  level,  this 
pressure  may  be  taken  as  14.7  Ib.  per  sq.  in.,  but  where  the  altitude 
is  considerable,  as,  for  instance,  at  Denver,  which  is  at  an  eleva- 
tion of  over  5000  ft.  above  the  sea,  a  closer  figure  should  be  taken. 
At  Denver,  12.5  Ib.  per  sq.  in.  would  be  proper. 

We  must  also  ascertain  what  the  average  atmospheric  tem- 
perature is  at  the  place  where  the  plant  is  located  and  estimate 
what  the  temperature  of  the  flue  gases  probably  will  be.  The 
last-mentioned  factor  will  depend  upon  the  design  of  the  boiler, 
arrangement  of  baffles,  cleanliness  of  the  heat-absorbing  surfaces, 
rate  of  combustion,  and,  somewhat,  upon  the  efficiency  of  combus- 
tion. On  an  average  the  flue-gas  temperature  ranges  between 
450  and  600  deg. 

In  our  present  example,  assume  that  the  atmospheric  pressure  is 
14.7  Ib.  per  sq.  in.,  the  atmospheric  temperature  is  70  deg.  F., 
and  the  temperature  of  the  flue  gases  500  deg.  F.  The  corre- 
sponding absolute  temperatures  are  530  and  960  deg.,  respectively. 

Substituting  in  the  formula,  then,  we  find  the  height  of  chimney 
required  to  develop  an  available  draft  of  0.71  in.  is 

H  =  —      1-25X0.71      _  0.8875 

o.52  X  14.7  ~ 


-  137.38  A 
or,  in  round  numbers,  140  ft.  above  the  grates. 


CHIMNEY  DESIGN  IOI 

DIAMETER  OF  CHIMNEY 

Having  determined  the  proper  height  of  chimney  for  a  given  set 
of  conditions  it  is  next  necessary  to  estimate  the  required  free 
cross-sectional  area.  For  this  the  following  formula  may  be  used: 

p 

E  =  J6^s~Vi 
where 

E  =  cross-sectional  area  of  the  chimney  in  square  feet; 

F  =  pounds  of  fuel  to  be  burned  per  hour; 

H  =  height  of  chimney  above  the  grates  in  feet. 

Applying  this  formula  to  our  example,  we  have 
7000  7000 

=  16.65  Vi^  ==  16.65  X  11.83  ==  3S'S  sq'fl' 


The  diameter  of  a  chimney  of  this  area  would  be  about  6  ft.  9  in. 
Chimneys  are  usually  built  circular  because  this  form  is  cheaper, 
more  stable  and  more  efficient  than  any  other.  It  is  cheaper 
because  less  material  is  required  for  a  chimney  of  a  given  cross- 
sectional  area;  more  stable  because  the  curved  surface  of  a  round 
chimney  offers  less  resistance  to  the  wind  than  the  flat  surface  of  a 
square  or  other  polygonal  (many-sided)  chimney;  also,  because 
structurally  the  circular  section  is  stronger.  A  circular  chimney 
is  more  efficient  because  the  resistance  to  the  flow  of  the  gases  is 
less  per  unit  of  sectional  area  and  the  amount  of  exposed  surf  ace  is 
less  than  with  any  other  shape  due  to  the  fact  that  the  circumfer- 
ence of  a  circle  is  shorter  than  the  perimeter  of  a  square  or  polygon. 

PRACTICE  PROBLEM 

By  way  of  exercise,  those  who  are  interested  may  work  out  the 
dimensions  of  a  chimney  for  the  following  conditions:  Eight 
500-hp.  boilers,  with  grates  83  sq.  ft.  in  area,  to  be  fired  with 
bituminous  slack,  the  combustion  of  4  Ib.  of  which  is  required 


102  FUEL  ECONOMY  AND  CO2  RECORDERS 

per  boiler  horsepower-hour.  At  times  the  boilers  will  be  over- 
loaded 25  per  cent.  The  breeching  is  50  ft.  long  from  the  chimney 
to  the  nearest  boiler  and  has  two  right-angle  turns  in  it.  The 
plant  is  located  about  2000  ft.  above  sea  level,  where  the  average 
atmospheric  pressure  is  13.57  lb.  per  sq.  in.  The  temperature 
of  the  outside  air  will  average  60  deg.  F.  and  that  of  the  flue 
gases  550. 

SOLUTION  OF  CHIMNEY  PROBLEM 
The  draft  required  for  the  breeching  is, 

(50  X  o.ooi)  +  (2  X  0.05)  =  0.15  in. 

which,  added  to  the  draft  required  by  the  boilers,  makes  a  total  of 
0.15  +  0.4  =  0.55  in. 

for  breeching  and  boilers.  The  rated  boiler  horsepower  of  the 
installation  is 

8  X  500  =  4000 

and  as  this  will  be  subject  to  a  25  per  cent,  overload  we  must 
provide  a  chimney  for 

4000  X  1.25  =  5000  hp. 

As  it  is  estimated  that  4  lb.  of  coal  will  be  required  to  develop  one 
boiler  horsepower,  the  total  maximum  consumption  will  be 

5000  X  4  =  20,000  lb.  per  hr. 
The  total  grate  area  is 

83  X  8  =  664  sq.  ft. 

Hence,  the  pounds  of  coal  burned  per  square  foot  of  grate  per 
hour  are 

20,000  -f-  664  =  30.12 


CHIMNEY  DESIGN  103 

And  the  draft  required  for  the  combustion  of  bituminous  slack  at 
the  rate  of  30  Ib.  per  sq.  ft.  of  grate  per  hour  is,  according  to 
the  table  given  on  page  97,  0.4  in.  of  water.  Then,  the  total 
available  draft  necessary  is 

0.55  +  0.4  =  0.95 

Applying  this  figure  in  the  formula  for  estimating  the  height  of 
chimney  we  have 


«-s«  X  13.5;  (—  - 

as  the  required  height  of  chimney  above  the  grates. 

Employing  the  formula  for  figuring  the  necessary  cross-sectional 
area  of  the  chimney  we  have 

*  -     20'000     =  89.44  *.  ft. 


l6.65Vi8o.47 
which  would  mean  a  chimney  10  ft.  8  in.  in  diameter. 


CHAPTER  VII 
EVAPORATION 

WATER 

Water  is  composed  of  the  two  gases,  hydrogen  and  oxygen 
combined  chemically  in  the  proportion  by  volume  of  two  parts 
of  hydrogen  and  one  part  of  oxygen.  The  chemical  formula  is 
H2O,  which  should  be  familiar  to  all  who  have  followed  this  series 
from  the  start,  as  water  is  the  product  formed  by  the  combustion 
of  the  hydrogen  found  in  such  fuels  as  coal,  oil,  gas,  etc.  The 
reaction  which  takes  place  was  explained  in  the  first  lesson  on 
combustion,  pages  i  and  2. 

Water  in  the  liquid  state  and  at  62  deg.  F.  weighs  62.355  Ib. 
per  cu.  ft.  Its  weight  or  volume  varies  with  changes  in  tem- 
perature. At  212  deg.  F.  the  weight  per  cubic  foot  is  59.76  Ib. 
and  at  32  deg.,  62.418  Ib.  Because  of  this  difference  in  weight  at 
different  temperatures,  circulation  can  be  established  by  applying 
heat.  The  water  in  the  bottom  of  a  system  expands  or  becomes 
lighter  when  heated  and  rises  or  is  forced  up  by  the  heavier  cold 
water  above,  which  flows  down  and  takes  its  place  and  in  turn  is 
heated  and  rises. 

BOILING  TEMPERATURE 

If  sufficient  heat  is  applied  to  water  in  its  liquid  state  it  will 
commence  to  boil.  This  boiling  results  in  some  of  the  water  being 
converted  into  a  vapor  which  is  called  steam,  and  if  the  boiling  is 
continued  all  the  liquid  will  be  changed  into  steam.  The  tem- 
perature at  which  water  will  boil  depends  upon  its  purity  and  the 
pressure  to  which  it  is  subjected.  Pure  water  in  an  open  vessel 
subjected  to  the  normal  atmospheric  pressure  at  sea  level  of 
14.7  Ib.  per  sq.  in.  boils  at  212  deg.  F.  The  common  impurities 

104 


EVAPORATION  105 

found  in  water  in  its  natural  states  tend  to  raise  the  boiling 
temperature.  Thus,  sea  water  which  contains  salt  as  its  principal 
impurity  will  not  boil  under  atmospheric  pressure  until  the  tem- 
perature reaches  213  deg.  or  a  little  higher,  depending  on  the 
exact  percentage  of  the  impurities  contained.  The  influence 
of  impurities  on  the  boiling  temperature  is  very  slight  (compared 
with  the  influence  of  pressure),  and  as  the  water  used  in  steam 
boilers  never  contains  but  a  comparatively  small  quantity  of 
impurities,  this  influence  is  customarily  neglected  in  steam-plant 
work. 

For  every  pressure  there  is  a  fixed  temperature  at  which  water 
boils.  The  higher  the  pressure  the  higher  the  boiling  point.  If 
the  temperature  of  boiling  water  or  of  the  steam  being  formed 
therefrom  is  known,  the  pressure  can  be  ascertained  without  a 
gage,  simply  by  referring  to  a  table  of  temperatures  and  pressures, 
as  these  always  correspond.  In  a  like  manner,  if  the  pressure  is 
known  the  temperature  can  be  determined  without  a  thermometer. 

The  same  principles  apply  when  water  freezes  to  form  ice. 
Pure  water  at  the  normal  atmospheric  pressure  at  sea  level 
(14.7  Ib.  per  sq.  in.)  freezes  at  32  deg.  F.  Impurities  tend  to 
lower  the  freezing  point.  Thus,  ordinary  sea  water  freezes  at 
about  27  deg.  The  higher  the  pressure  the  lower  the  freezing 
point. 

When  water  is  undergoing  the  process  of  boiling  the  steam 
formed  has  the  same  pressure  and  temperature  as  the  boiling 
water  from  which  it  is  being  formed  or  evaporated.  Such  steam 
is  known  as  saturated  steam. 

Now,  if  heat  is  applied  to  the  steam  itself  and  the  containing 
apparatus  is  arranged  in  such  a  manner  that  the  steam  is  not 
in  close  contact  with  water  and  hence  cannot  impart  this  extra 
heat  to  the  water  to  form  more  steam,  the  temperature  and 
pressure  will  both  tend  to  rise.  But  the  new  temperature  of 
the  steam  will  not  correspond  with  the  boiling  temperature  of 
water  at  a  pressure  equal  to  the  new  pressure  of  the  steam.  The 
temperature  will  be  higher.  Such  steam  is  called  superheated 
steam. 


io6  FUEL  ECONOMY  AND  CO2  RECORDERS 

To  sum  up,  then,  the  boiling  point  of  water  depends  upon 
the  pressure;  the  boiling  temperature  is  fixed  and  unchangeable 
for  any  given  pressure.  Saturated  steam  is  steam  that  has  the 
same  temperature  as  boiling  water  under  equal  pressure.  Super- 
heated steam  is  steam  that  has  a  higher  temperature  than  boiling 
water  under  the  same  pressure. 

Saturated  steam  may  be  dry  or  wet.  Dry  saturated  steam  is 
steam  that  has  been  thoroughly  evaporated  and  does  not  carry 
any  drops,  globules,  or  particles  whatsoever  of  liquid  water  in 
the  form  of  a  spray  or  mist.  A  clearer  and  more  definite  ex- 
planation of  the  difference  between  dry  and  wet  steam  will  be 
given  later. 

EVAPORATION 

Ebullition  is  the  name  sometimes  given  to  the  process  of 
boiling  or  steam  generation;  a  commoner  name  is  evaporation. 
We  speak  of  the  evaporation  per  pound  of  coal,  equivalent  eva- 
poration, etc.  Then,  there  is  another  term  often  used:  vapor- 
ization, the  process  of  changing  from  a  liquid  to  a  vapor,  that 
is,  of  changing  from  liquid  water  to  steam.  Although  the  last 
two  terms  really  mean  the  same  thing,  custom  has  established  a 
slight  distinction.  Evaporation  has  come  to  mean  the  whole 
process  of  making  steam,  starting  with  the  warming  up  of  the 
feed  water  to  the  boiling  temperature  and  including  the  actual 
conversion  of  the  water  into  steam,  while  vaporization  has  come 
to  be  considered  simply  the  actual  conversion  from  water  at  the 
boiling  point  into  steam  at  the  same  temperature  and  pressure. 

LATENT  HEAT 

When  we  apply  heat  to  a  body  we  instinctively  think  of  an 
accompanying  rise  in  temperature.  For  instance,  if  we  apply 
heat  to  a  piece  of  iron  we  know  that  the  temperature  of  the  iron 
quickly  goes  up.  When  we  apply  heat  to  water,  say,  at  60  deg., 
the  water  grows  warmer — its  temperature  rises.  The  water 
will  continue  to  get  hotter,  the  more  heat  we  add,  until  the  boiling 
point  is  reached.  If  the  water  is  in  an  open  vessel  and  at  sea 


EVAPORATION  107 

level  this  point  will  be  at  the  212  deg.  mark.  Now,  right  here  a 
strange  thing  will  occur.  »  The  water  will  fail  to  get  any  hotter. 
No  matter  how  much  heat  we  apply,  no  matter  how  hard  we  force 
the  fire  or  how  high  we  turn  the  gas  burner,  whichever  it  happens 
to  be,  the  thermometer  will  stick  at  212  deg.  If  you  doubt  this, 
try  the  experiment  with  a  pan  of  water  and  thermometer  and 
convince  yourself. 

The  water  will  cease  getting  hotter,  but  at  the  same  time  some- 
thing else  will  happen.  The  instant  the  boiling  point  is  reached 
ebullition — the  process  of  steam  generation — will  set  in.  The 
question  naturally  arises:  If  the  temperature  cannot  be  increased 
by  applying  more  heat,  what  becomes  of  this  extra  heat?  It  is 
used  in  converting  the  liquid  water  into  steam.  As  soon  as  the 
heat  is  shut  off  the  boiling  or  steam-making  will  cease,  proving 
that  heat  is  required  to  convert  the  water  from  the  liquid  into  the 
vaporous  state.  The  more  heat  we  apply  the  more  rapid  will 
be  the  rate  of  steam  generation. 

It  requires  970.4  B.t.u.  to  change  i  Ib.  of  water  at  atmospheric 
pressure  and  a  temperature  of  212  deg.  into  steam  at  the  same 
temperature.  Just  why  so  much  heat  is  used  up  or  absorbed 
without  causing  a  rise  in  temperature  when  water  is  broken  up 
into  steam  I  will  not  attempt  to  explain  here.  The  only  really 
important  thing  to  know  is  that  such  is  the  case.  The  heat  thus 
absorbed  is  called  latent  heat  of  vaporization  or  the  latent  heat 
of  steam.  The  term  latent  means  hidden  or  secret.  Hence, 
the  latent  heat  of  steam  is  the  heat  that  is  taken  up  and  hidden 
by  the  water  when  it  changes  from  its  liquid  to  its  vaporous  state. 
We  consider  the  heat  as  being  latent  or  hidden  because  we  can 
see  no  evidence  of  its  having  gone  into  the  steam  as  far  as  the 
thermometer  can  tell  us. 

When  steam  condenses  the  heat  transfer  is  the  other  way. 
If  a  pound  of  steam  at  atmospheric  pressure  were  injected  into  a 
tank  containing  99  Ib.  of  water  at,  say,  60  deg.,  so  that  all  the 
steam  condensed  back  into  water,  the  temperature  of  the  resulting 
100  Ib.  of  water  would  be  71.2  deg.,  showing  a  rise  of  11.2  deg.  for 
the  original  99  Ib.  of  water. 


io8       FUEL  ECONOMY  AND  CO2  RECORDERS 

The  temperature  of  steam  at  atmospheric  pressure  is  212  deg. 
Hence,  the  drop  in  temperature  was  only 

212  —  71.2  =  140.8  deg. 

But  the  99  Ib.  of  water  rose  11.2  deg.,  showing  that 
99  X  ii. 2  =  1108.8  B.t.u. 

were  imparted  to  it.     (One  B.t.u.  being  the  amount  of  heat 
required  to  raise  the  temperature  of  i  Ib.  of  water  i  deg.) 

If  the  steam  had  been  condensed  before  it  was  injected  into 
the  99  Ib.  of  water  so  that  it  went  in  as  a  liquid  at  212  deg.  in- 
stead of  a  vapor  at  212  deg.,  the  rise  in  temperature  of  the  99  Ib. 
would  be  only  1.52  deg.  because  the  pound  of  condensed  steam 
or  water  ait  212  had  only 

212  —  60  =  152  B.t.u. 

more  in  it  than  a  pound  of  the  cooler  water. 

Some,  who  are  just  beginning  the  study  of  evaporation  and 
steam,  may  experience  a  little  difficulty  in  realizing  that  steam 
has  weight,  and,  hence,  may  be  slightly  confused  when  they 
come  in  contact  with  such  terms  as  pounds  of  steam,  etc.  This 
confusion  is  all  the  more  likely  because  the  pressure  is  also  spoken 
of  in  terms  of  pounds. 

In  an  earlier  lesson  (page  7)  it  was  shown  that  a  gas  has 
weight,  and  in  the  same  manner  it  could  easily  be  demon- 
strated that  steam  has  weight.  In  fact,  the  weight  of  steam  can 
be  ascertained  more  easily  than  the  weight  of  a  gas;  all  that  is 
necessary  is  to  condense  the  steam  and  weigh  the  resulting  water. 
In  referring  to  a  quantity  or  weight  of  steam  the  word  "of" 
is  employed.  Thus,  we  say,  9  Ib.  of  steam  evaporated  per  pound 
of  coal.  Which  means  that  the  combustion  of  a  pound  of  coal 
has  caused  the  evaporation  of  9  Ib.  of  water,  resulting  in  the 
generation  of  9  Ib.  of  steam.  •* 

In  referring  to  pressure  we  use  the  word  "at."  Thus,  steam 
at  150  Ib.  Which  means  steam  which  causes  or  possesses  a  pres- 
sure of  150  Ib.  on  each  square  inch  of  the  surface  confining  it. 


EVAPORATION  109 

JSTEAM  TABLES 

The  boiling  temperature  of  water  is  different  for  different  pres- 
sures. Thus,  at  atmospheric  pressure  (14.7  Ib.  per  sq.  in.  ab- 
solute, or  zero  gage)  the  boiling  temperature  is  212  deg.  F.,  while 
at  i5o-lb.  gage  it  is  365.9  deg.  The  higher  the  pressure,  the 
higher  the  boiling  temperature. 

In  addition,  the  latent  heat,  or  the  quantity  of  heat  required  to 
convert  a  pound  of  the  water  from  its  liquid  to  vaporous  form, 
varies  quite  extensively  with  variation  in  pressure.  Thus,  the 
latent  heat  of  steam  at  atmospheric  pressure  is  970.4  B.t.u.  per 
pound,  while  at  i5o-lb.  gage  it  is  only  856.9  B.t.u.,  or  more  than 
loo  B.t.u.  less  per  pound.  The  higher  the  pressure,  the  lower  the 
latent  heat. 

The  volume  of  a  pound  of  steam  varies  greatly  with  variation  in 
pressure.  At  atmospheric  pressure  i  Ib.  of  steam  has  a  volume  of 
26.79  cu.  ft.,  while  at  i5o-lb.  gage  the  volume  is  only  2.758  cu.ft., 
or  only  about  one-tenth  as  much.  The  higher  the  pressure  the 
smaller  the  volume  per  unit  of  weight.  It  is  this  characteristic  of 
the  steam  that  makes  it  suitable  for  use  in  engines,  turbines,  etc. 
The  steam  is  generated  at  a  high  pressure  with  a  small  volume  per 
unit  of  weight,  then  let  into  the  cylinder  or  turbine  stage  where  its 
pressure  forces  the  piston  ahead — provided  the  resistance  of  the 
piston  is  not  greater  than  the  pressure  of  the  steam,  which  is  the 
case  when  the  engine  is  on  dead  center  or  when  it  is  too  heavily 
loaded. 

As  the  pressure  of  the  steam  forces  the  piston  forward,  more 
room  is  created  in  the  cylinder  and  the  pressure  is  slightly  relieved 
or  lowered.  As  the  pressure  lowers,  the  steam  must  expand  to 
fill  the  increased  space  because  for  every  pressure  there  is  a 
corresponding  volume  just  the  same  as  for  every  pressure  there  is 
a  corresponding  boiling  temperature,  latent  heat,  etc.  And  the  re- 
lation of  these  quantities  to  each  other  never  varies  so  long  as  steam 
is  steam.  They  must  fulfill  Nature's  laws,  which  are  immutable 
— cannot  be  repealed  or  changed. 

However,  this  action  of  steam  in  the  cylinder  of  an  engine 


HO  FUEL  ECONOMY  AND  CO2  RECORDERS 

is  a  little  off  the  subject  now  occupying  our  attention,  and  a 
more  thorough  study  of  it  will  be  offered  in  its  proper  turn 
later  on. 

Because  the  boiling  temperature,  latent  heat,  etc.,  are  different 
for  each  different  pressure,  we  have  what  are  called  the  steam 
tables,  or,  to  be  more  exact,  tables  of  the  properties  of  saturated 
steam.  These  are  exceedingly  convenient  for  finding  the  other 
factors  when  any  one  is  known,  and  it  behooves  all  who  intend  to 
continue  on  in  power-plant  study  and  work  to  become  familiar 
with  the  tables. 

A  modified  and  condensed  form  of  the  latest  accepted  steam 
tables  is  presented  herewith.  The  original  tables  were  compiled 
by  Professors  Lionel  S.  Marks  and  Harvey  N.  Davis,  and  pub- 
lished by  Longman,  Green  &  Co.,  through  whose  courtesy  we  are 
permitted  to  publish  Table  3,  herewith. 

GAGE  AND  ABSOLUTE  PRESSURE 

In  the  first  column  of  the  table  are  given  the  vacuum  and  gage 
pressures;  in  the  second,  absolute  pressures.  In  the  first  para- 
graph of  this  lesson  you  may  have  noticed  that  atmospheric 
pressure  was  given  as  14.7  Ib.  per  sq.  in.,  absolute,  or  zero  gage. 
This  was  done  because  in  these  modern  days  there  are,  un- 
fortunately, two  standards  of  pressure  measurement.  Gage 
pressure  takes  its  name  from  the  instrument  commonly  used  for 
measuring  boiler  steam  pressure.  Now,  the  ordinary  pressure 
gage  used  on  a  boiler  does  not  indicate  the  total  pressure  actually 
existing  inside  the  boiler.  It  only  measures  the  difference  between 
the  pressure  of  the  steam  within  the  boiler  and  the  pressure  of  the 
atmosphere  without. 

This  is  due  to  the  construction  of  the  gage,  which  consists 
principally  of  a  curved  hollow  metal  tube  open  at  one  end.  The 
hollow  interior  of  the  tube  connects  at  the  open  end  with  the 
interior  of  the  boiler  while  the  exterior  of  the  tube  is  exposed  to  the 
pressure  of  the  atmosphere.  When  the  pressure  acting  on  the 
inside  of  the  tube  is  equal  to  the  atmospheric  pressure  acting  on 


EVAPORATION  in 

the  outside,  the  tube  is  in  its  normal  position  and  the  pointer  on 
the  dial  of  the  gage,  connected  to  the  tube  at  the  closed  end, 
indicates  zero  on  the  scale.  When  the  pressure  within  exceeds 
the  atmospheric  pressure  without,  the  tube  tends  to  lose  its  curve 
and  straighten  out.  And  as  the  closed  end,  to  which  the  pointer 
is  attached,  is  the  only  end  free  to  move,  the  change  in  the 
position  of  the  tube  is  all  transmitted,  through  suitable  mechan- 
ism, to  the  pointer.  This  swings  away  from  the  zero  mark  and 
points  to  the  position  on  the  scale  corresponding  with  the  pres- 
sure existing  in  the  boiler  over  and  above  that  of  the  atmosphere 
outside. 

Absolute  pressure  means  the  total  pressure  actually  existing 
in  the  space  where  the  measurement  is  taken  whether  this  be  in  a 
boiler,  a  condenser,  in  the  open  atmosphere  or  anywhere  else. 
It  does  not  take  into  account  any  outside  pressure  that  may 
happen  to  be  acting  on  the  measuring  gage  or  instrument.  Hence, 
the  zero  point  on  the  absolute-pressure  scale  is  at  absolute  vacuum. 
If  a  whole  boiler,  pressure  gage  and  all,  were  inclosed  in  a  vacuum, 
the  gage  would  then  show  absolute  pressures  because,  there  being 
absolutely  no  pressure  outside,  the  difference  between  the  inside 
and  outside  pressures  would  equal  the  total  pressure  actually 
existing  inside  the  boiler. 

The  absolute-pressure  system  of  measurement  is  the  more 
accurate  one  because  it  is  not  dependent  upon  the  more  or  less 
variable  pressure  of  the  atmosphere.  An  absolute-pressure  gage  is 
more  complicated  and  expensive,  however,  than  the  ordinary  gage 
used  in  boiler  work,  and,  hence,  far  less  popular.  So,  in  actual 
steam-plant  operation  gage  pressures  are  the  ones  mainly  en- 
countered. But  gage  pressures  can  easily  be  translated  into  ab- 
solute pressures-  by  adding  the  amount  of  atmospheric  pressure 
existing  at  the  location  of  the  plant  under  consideration.  Thus,  at 
sea  level,  absolute  pressure  may  be  taken  as  gage  pressure  plus 
14.7  Ib.  per  square  inch.  At  a  higher  altitude  than  sea  level,  the 
atmosphric  pressure  is  less;  hence,  care  must  be  used,  in  cases 
where  the  difference  is  appreciable,  that  the  proper  value  be 
employed.  For  instance,  at  Denver  the  average  atmospheric 


112 


FUEL  ECONOMY  AND  CO2  RECORDERS 


TABLE  3.—  PROPERTIES  OF  .SATURATED  STEAM 
From  Marks  &  Davis'  Tables.     Courtesy  of  Longmans,  Green  &  Co. 


Total  heat  above 
32°  F. 


I 
Vacuum, 
in.  of 
mercury 

2 

Absolute 
pressure, 
Ib.  per 
sq.  in. 

Tempera- 
ture, 
degrees 
Fahr. 

Heat4  of 
the  iquid 

B.t.u. 

In  the 
steam 
H 
B.t.u. 

6 

Latent 
heat 
L  =  H-h 
B.t.u. 

Volume 
cu.  ft.  in 
i  Ib.  of 
steam 

8 

Weight  of 

I   CU.  ft. 

of  steam, 
Ib. 

27.88 

I 

101.83 

69.8 

1104.4 

1034.6 

333-0 

0.00300 

2S-8S 

2 

126.15 

94.0 

1115.0 

I02I.O 

173-5 

0.00576 

23.81 

3 

141.52 

109.4 

II2I  .6 

IOI2.3 

118.5 

o  .  00845 

21.78 

4 

153-01 

120.9 

1126.5 

1005.7 

90.5 

0.01107 

19-74 

5 

162.28 

130.1 

1130.5 

1000.3 

73-33 

0.01364 

17.70 

6 

J7o.o6 

137-9 

"33-7 

995-8 

61.89 

o.  01616 

I5-67 

7 

176.85 

144-7 

"36.5 

991.8 

53.56 

0.01867 

I3-63 

8 

182.86 

150.8 

1139.0 

988.2 

47-27 

0.02115 

1  1.  60 

9 

188.27 

156.2 

1141.1 

985.0 

42.36 

0.02361 

9-56 

10 

193.22 

161  .1 

1143.1 

982.0 

38-38 

0.02606 

7-52 

ii 

197-75 

165.7 

1144.9 

979-2 

35-10 

0.02849 

5-49 

12 

201.96 

169.9 

1146.5 

976.6 

32.36 

0.03090 

3-45 

13 

205.87 

173-8 

1148.0 

974-2 

30.03 

0.03330 

1.42 

14 

209.55 

177-5 

1149.4 

971.9 

28.02 

0.03569 

Lb. 

gage 

press 

0 

14-7 

212.  0 

180.0 

1150.4 

970.4 

26.79 

0.03732 

5-3 

20 

228.0 

196.1 

1156.2 

960.0 

20.08 

o  .  04980 

10.3 

25 

240.1 

208.4 

1160.4 

952.0 

16.30 

0.0614 

15-3 

30 

250.3 

218.8 

1163.9 

945-.  i 

13-74 

0.0728 

20.3 

35 

259-3 

227.9 

1166.8 

938.9 

11.89 

0.0841 

25-3 

40 

267.3 

236.1 

1169.4 

933-3 

10.49 

0.0953 

30.3 

45 

274-5 

243-4 

1171.6 

928.2 

9-39 

0.1065 

35-3 

50 

28l.O 

250.1 

1173.6 

923.5 

8.5i 

0.1175 

40.3 

55 

287.1 

256.3 

II75-4 

919.0 

7.78 

0.1285 

45-3 

60 

292.7 

262.  i 

1177.0 

914.9 

7.17 

0.1394 

50-3 

65 

298.0 

267.5 

1178.5 

911.0 

6.65 

0.1503 

55-3 

70 

302.9 

272.6 

1179.8 

907.2 

6.  20 

o.  1612 

60.3 

75 

307.6 

277-4 

1181.1 

903.7 

5-8i 

0.1721 

65.3 

80 

312.0 

282.0 

1182.3 

900.3 

5-47 

o.  1829 

70.3 

85 

316.3 

286.3 

1183.4 

897-1 

5-i6 

0.1937 

75-3 

90 

320.3 

290.5 

1184.4 

893.9 

4-89 

0.2044 

80.3 

95 

324.1 

294-5 

1185.4 

890.9 

4-65 

0.2151 

85.3 

100 

327.8 

298.3 

1186.3 

888.0 

4.429 

0.2258 

EVAPORATION 


TABLE  3.— PROPERTIES  OF  SATURATED  STEAM.— Continued 

Total  heat  above 
32°  F. 


I 
Vacuum 
in.  of 
mercury 

2 

Absolute 
pressure, 
Ib.  per 
sq.  in. 

3 

Tempera- 
ture, 
degrees 
Fahr. 

Heat  of 
the  liquid 

B.t.u. 

In  the 
steam 
H 
B.t.u. 

6 

Latent 
heat 
L  =  H-h 
B.t.u. 

Volumne 
cu.  ft.  in 
I  Ib.  of 
steam 

8 

Weight  of 

I  CU.  ft. 

of  steam, 
Ib. 

Lb. 

gage 

press 

90-3 

105 

331-4 

302.0 

1187.2 

885.2 

4.230 

0.2365 

95-3 

no 

334-8 

305.5 

1188.0 

882.5 

4.047 

0.2472 

100.3 

US 

338.1 

309-0 

1188.8 

879.8 

3.880 

0-2577 

105-3 

120 

341-3 

312.3 

1189.6 

877-2 

3.726 

0.2683 

II0.3 

125 

344-4 

315.5 

1190-3 

874.7 

3.583 

0.2791 

II5-3 

130 

347-4 

318.6 

1191.0 

872.3 

3-452 

0.2897 

120.3 

135 

350-3 

321.7 

1191.6 

869.9 

3.331 

0.3002 

I2S.3 

140 

353-1 

324.6 

1192.2 

867.6 

3.219 

0.3107 

130.3 

US 

355-8 

327.4 

1192.8 

865.4 

3-  "2 

0.3213 

135-3 

150 

358.5 

330.2 

"93-4 

863.2 

3.012 

0.3320 

140.3 

155 

361.0 

332.9 

1194.0 

861.0 

2.92O 

0.3425 

145-3 

1  60 

363-6 

335-6 

"94-5 

858.8 

2-834 

0.3529 

150.3 

165 

366.0 

338.2 

1195-0 

856.8 

2-753 

0.3633 

155-3 

170 

368.5 

340.7 

H95.4 

854.7 

2.675 

0-373S 

160.3 

175 

370.8 

343-2 

H95.9 

852.7 

2.602 

0.3843 

165.3 

1  80 

373-1 

345-6 

1196.4 

850.8 

2-533 

0.3948 

175-3 

190 

377-6 

350-4 

"97.3 

846.9 

2.406 

0.4157 

185-3 

200 

381.9 

354-9 

1198.1 

843.2 

2.290 

0-437 

195-3 

210 

386.0 

359-2 

1198.8 

839-6 

2.187 

0-457 

200.3 

215 

388.0 

361.4 

1199.2 

837.9 

2.381 

0.468 

pressure  is  but  12.5  Ib.  per  square  inch.  Consequently,  the  first 
colume  of  Table  3  would  be  over  2  Ib.  out  of  the  way  and  should 
not  be  used  for  accurate  work.  The  thing  to  do  in  such  cases  is 
to  translate  into  absolute  pressures  and  use  the  second  column. 
For  most  ordinary  purposes,  however,  the  errors  caused  are  hardly 
important  enough  to  warrant  any  large  amount  of  extra  work. 

The  third  column  of  Table  3  gives  the  temperature  of  the 
steam  at  various  pressures.  This  temperature  is  also  the  boiling 
temperature  of  water  under  the  corresponding  pressure,  as  was 
carefully  explained  on  page  104. 


114  FUEL  ECONOMY  AND  CO2  RECORDERS 

HEAT  OF  THE  LIQUID 

In  the  fourth  column  is  given  the  heat  of  the  liquid,  or,  as  it  is 
sometimes  called,  the  heat  in  the  water.  The  figures  in  this 
column  represent  the  number  of  B.t.u.  required  to  raise  the  tem- 
perature of  i  Ib.  of  water  from  3  2  deg.  to  the  boiling  temperature 
at  the  pressure  given.  Thus,  at  atmospheric  pressure  or  zero, 
gage,  the  heat  of  the  liquid  is  180  B.tu.  This  can  be  easily 
checked  from  the  knowledge  gained  from  previous  lessons.  It 
was  learned  by  definition  that  it  takes  i  B.t.u.  to  raise  the  tem- 
perature of  i  Ib.  of  water  i  deg.  Then,  as  there  are  212  —  32 
=  1 80  deg.  difference  between  32  and  the  boiling  point,  it  must 
require  180  X  i  =  180  B.t.u.  to  raise  i  Ib.  of  water  from  32  deg. 
to  the  boiling  temperature  at  atmospheric  pressure. 

As  the  pressure  grows  higher,  the  heat  of  the  liquid  does  not 
exactly  correspond  with  the  number  of  degrees  difference  between 
32  and  the  boiling  point..  Thus,  at  35-3-lb.  gage,  or  5o-lb., 
absolute,  pressure,  the  number  of  B.tu.  required  to  raise  the 
temperature  of  i  Ib.  of  water  from  32  deg.  to  the  boiling  point  (the 
heat  of  the  liquid)  is  i.i  greater  than  the  number  of  degrees  be- 
tween those  two  points.  This  is  because  the  heat  required  to 
raise  the  temperature  of  i  Ib.  of  water  i  deg.  increases  gradually 
as  the  pressure  increases  above  14.7  Ib.  per  square  inch. 

In  the  sixth  column  of  Table  3  are  given  the  values  of  latent 
heat  of  steam  at  the  various  pressures. 

TOTAL  HEAT  IN  STEAM 

The  figures  in  column  5  are  the  sums  of  the  figures  in  columns 
4  and  6  and  they  show  the  total  heat  contained  in  i  Ib.  of  steam 
above  the  temperature  of  3  2  deg. 

It  may  be  a  source  of  wonder  to  some  why  columns  4  and  5  are 
headed  "Total  Heat  Above  32  Deg.,  F."  The  explanation  is 
this: 

Every  substance,  no  matter  what  its  temperature,  contains 
some  heat.  We  think  of  a  piece  of  ice  as  a  pretty  cold  chunk  of 


EVAPORATION  115 

solid  water  and  would  hardly  suspect,  on  first  thought,  that  it 
could  have  any  heat  concealed  about  it.  Yet,  a  pound  of  ice 
just  at  the  freezing  point  (32  deg.)  possesses  16  B.t.u.  more  than  a 
pound  at  zero  temperature.  Ice  may  possess  different  tempera- 
tures just  the  same  as  water,  steel  or  steam.  Then,  ice  at  zero  is 
certainly  colder  than  ice  at  3  2  deg.  and,  vice  versa,  ice  at  3  2  deg  . 
must  be  warmer  than  ice  at  zero,  and  hence  it  must  possess  more 
heat. 

In  fact,  no  matter  how  cold  you  may  make  a  substance,  it  still 
must  possess  some  heat.  Suppose  you  refrigerated  a  piece  of 
ice  until  its  temperature  went  down  to  —75  deg.,  in  all  loy-deg. 
below  the  normal  freezing  point  of  water.  That  would  be  pretty 
cold,  wouldn't  it?  Yet  that  ice  could  be  refrigerated  still  more, 
say,  to  —loo  deg.,  showing  that  even  at  —75  deg.  it  hadn't  yet 
lost  all  the  heat  it  possessed. 

Man  has  not  yet  discovered  just  what  the  absolutely  lowest 
temperature  is.  He  has  succeeded  in  obtaining  artificially  some 
very  low  degrees,  but  he  has  never  reached  the  lowest  limit 
because  his  apparatus  fails  first. 

Then,  in  view  of  the  fact  that  we  do  not  know  at  just  what 
temperature  the  point  of  complete  lack  of  heat  exists,  we  must 
establish  a  "base"  line  to  work  from  when  we  talk  of  or  deal 
with  quantities  involving  "total"  heat.  In  dealing  with  steam, 
this  base  line  is  the  freezing  point  of  water  under  atmospheric 
pressure,  or  3  2  deg.  F.  Thus,  the  total  heat  of  the  liquid  or  in  the 
water  is  the  heat  that  must  be  imparted  to  i  Ib.  of  water  in  order 
to  raise  its  temperature  from  32  deg.  to  the  boiling  point.  And 
the  total  heat  in  the  steam  is  this  quantity  plus  the  latent  heat. 

Column  7  gives  the  volume  of  i  Ib.  of  steam  in  cubic  feet  and 
column  8  the  weight  of  i  cu.  ft.  in  pounds. 

EQUIVALENT  EVAPORATION 

By  referring  to  Table  3  it  will  be  noticed  that  the  total  heat  in 
a  pound  of  steam  gradually  increases  as  the  pressure  increases. 
Thus,  at  atmospheric  pressure  the  total  heat  of  a  pound  of  steam 


Il6  FUEL  ECONOMY  AND  CO2  RECORDERS 

is  1150.4  B.t.u.,  while  at  165  lb.,  abs.,  it  is  1195  B.t.u.  The 
heat  required  to  generate  steam  at  a  pressure  of  125  lb.  abs., 
starting  with  feed  water  at  100  deg.,  is  1122.3  B.t.u.  The  proof 
is  this:  The  total  heat  above  32  deg., as  shown  by  the  steam  table 
is  1190.3  B.t.u.  But  68  B.t.u.  were  already  in  the  water  because 
we  started  with  the  water  at  100,  instead  of  at  32  deg.,  and  as  i 
B.t.u.  will  raise  the  temperature  of  i  lb.  of  water  i  deg.,  it  is 
evident  that  (100  —  32)  X  i  =  68  B.t.u.  had  already  been 
supplied. 

Then,  the  heat  required  to  generate  a  pound  of  steam  depends 
upon  the  pressure  at  which  the  steam  is  to  be  generated  and  the 
temperature  of  the  feed  water.  It  seldom  happens  that  two  boiler 
plants  are  exactly  alike  in  both  of  these  respects  and,  hence, 
when  the  performance  of  one  plant  is  being  compared  with  that  of 
another,  in  order  to  be  fair,  it  is  necessary  to  have  a  common 
ground  for  comparison.  One  engineer  might  state,  "I  get  an 
actual  evaporation  of  10.5  lb.  of  water  per  pound  of  coal,"  mean- 
ing that  for  every  pound  of  coal  fired  into  the  furnace,  10.5  lb. 
of  water  were  actually  evaporated  into  steam  under  the  conditions 
existing  in  his  plant.  He  might  think  that  he  was  making  a 
better  showing  than  his  neighbor,  who,  although  using  exactly 
the  same  grade  of  coal,  was  getting  an  actual  evaporation  of  10 
lb.  per  pound  of  coal.  Yet,  when  the  boiler  pressure  and  feed- 
water  temperature  in  both  plants  are  taken  into  consideration, 
it  might  be  shown  that  the  man  in  the  other  plant  was  securing 
better  efficiency  even  though  the  quantity  of  water  actually 
evaporated  per  pound  of  fuel  was  somewhat  less. 

Assume  that  in  the  first-mentioned  plant  the  steam  pressure 
carried  was  115  lb.  per  sq.  in.,  abs.,  and  the  temperature  of  the 
feed  water  was  200  deg.,  while  in  the  second  plant  the  pressure 
was  190  lb.,  abs.,  and  the  feed- water  temperature  100  deg. 

In  the  first  plant,  the  heat  required  to  generate  a  pound  of 
steam  was 

Total  Heat  in  Heat  in 

the  Steam  Feed  Water 

Above  32  Deg.  Above  32  Deg. 

1188.8  168  =     1020.8  B.t.u. 


EVAPORATION  117 

And  in  the  second  plant  the  required  heat  was 

Total  Heat  in  Heat  in 

the  Steam  Feed  Water 

Above  32  Deg.  Above  32  Deg. 

1197.3  68  =     1129.3  B.t.u. 

In  the  first  plant  10.5  Ib.  of  water  were  actually  evaporated 
per  pound  of  coal.  Then,  of  the  heat  liberated  by  the  combustion 
of  i  Ib.  of  coal 

1020.8  X  10.5  =  10,718  B.t.u. 

were  absorbed  by  the  boiler  and  went  toward  useful  work  by 
generating  steam. 

In  the  other  plant,  10  Ib.  of  water  were  actually  evaporated 
per  pound  of  coal,  yet 

1129.3  X  10  =  11,293  B.t.u. 

or  575  B.t.u.  more  were  absorbed  and  went  toward  useful 
work  than  in  the  first  case.  Consequently,  as  the  same  quality 
of  coal  was  used  in  each  case,  the  efficiency  of  the  latter  plant 
was  higher  than  the  former. 

This  example  emphasizes  the  importance  of  having  a  standard 
method  of  comparison  so  that  the  performance  of  all  plants,  no 
matter  how  widely  the  feed-water  temperature  and  the  steam 
pressure  may  vary,  can  be  compared  with  complete  fairness. 
The  method  used  is  to  calculate  the  number  of  pounds  of  water 
that  could  be  evaporated  from  a  feed  temperature  of  212  deg. 
into  steam  at  the  same  temperature  by  the  heat  used  in  evaporat- 
ing i  Ib.  of  water  from  the  feed  temperature  used  in  the  plant 
discussed  into  steam  at  the  pressure  actually  employed  in  that 
plant.  The  ratio  of  the  evaporation  at  212  deg.  to  the  actual  is 
called  the  "factor  of  evaporation."  And  when  the  number  of 
pounds  of  water  actually  evaporated  is  multiplied  by  the  factor 
of  evaporation  the  product  is  the  "equivalent  evaporation" 
or  the  evaporation  "from  and  at  212  deg." 

The  factor  of  evaporation  may  be  found  by  the  simple  formula 


p  . 

970.4 


Ii8  FUEL  ECONOMY  AND  CO2  RECORDERS 

where 

F  =  factor  of  evaporation; 
H  =  total  heat  in  the  steam  above  32  deg.; 
/  =  temperature  of  the  feed  water. 

Applying  this  formula  to  the  first  plant  mentioned  in  the 
example  just  given,  the  factor  of  evaporation  is  found  to  be 

P  =      (H88.8   -    200)   +   3*    m    x 
970.4 

Multiplying  together  the  pounds  of  water  actually  evaporated 
per  pound  of  coal  and  the  factor  of  evaporation,  we  have 

10.5  X  1.052  =  11.05  lb., 

the  equivalent  evaporation  per  pound  of  coal.  This  quantity 
is  called  the  equivalent  evaporation  because  the  heat  put  into 
11.05  lb.  of  water  at  212  deg.  to  make  steam  at  212  deg.  (at- 
mospheric, or  14.7  lb.,  abs.,  pressure)  is  exactly  the  same  as  the 
heat  put  into  the  10.5  lb.  at  200  deg.  to  make  steam  at  115  lb., 
abs.,  pressure.  Hence,  the  two  quantities  are  equivalent  from 
the  standpoint  of  heat. 

BOILER  HORSEPOWER 

The  name  horsepower  was  originally  applied  to  the  steam 
engine.  James  Watt,  who  did  great  work  in  the  eighteenth 
century  developing  the  steam  engine,  rated  his  engines  as  being 
able  to  do  as  much  work  as  a  certain  number  of  work  horses,  hence, 
the  unit,  horsepower,  which  has  been  employed  ever  since. 
When  it  became  desirable  to  apply  a  unit  to  the  output  or  ca- 
pacity of  a  boiler,  the  same  name  was  employed.  Thus,  a  boiler 
which  could  supply  steam  enough  to  operate  a  loo-hp.  engine 
was  called  a  loo-hp.  boiler.  But  such  a  standard  without  further 
qualification  was  very  indefinite  indeed.  First,  because  vari- 
ous types  and  sizes  of  steam  engines  require  widely  different 
quantities  of  steam  per  horsepower-hour,  and  second,  because  a 
boiler  of  given  dimensions  may  be  made  to  generate  steam  at  a 
greatly  varying  rate,  depending  on  how  hard  the  fire  is  forced. 


EVAPORATION  119 

Finally,  an  exact  standard  was  selected  and  a  boiler  horse- 
power was  established  as  the  evaporation  of  30  Ib.  of  water  per 
hour  from  a  feed  temperature  of  100  deg.  into  steam  at  a  pressure 
of  70  Ib.  gage,  or  the  equivalent  evaporation  of  34.5  Ib.  of  water 
per  hour  from  and  at  212  deg.  This  standard  suffices  to  de- 
termine the  output  of  a  boiler  when  in  operation,  but  it  gives  no 
means  of  determining  the  dimensions  of  a  boiler  for  a  given  duty. 
In  other  words,  a  man  who  wished  to  purchase,  say,  a  2oo-hp. 
boiler,  had  no  means  by  which  he  could  calculate  the  area  of  the 
heating  surface  the  boiler  should  possess  and,  hence,  he  was  forced 
to  depend  upon  the  manufacturer's  judgment.  To  avoid  confu- 
sion and  misunderstanding,  it  was,  therefore,  necessary  to  establish 
a  standard  for  the  area  of  heating  surface  necessary  to  develop 
one  boiler-horsepower.  At  present,  this  standard  is  generally  ac- 
cepted as  10  sq.  ft.  Thus,  if  a  man  purchases  a  boiler  of  i5o-hp. 
rating,  he  expects  to  get  a  unit  of  such  dimensions  as  to  possess 
1500  sq.  ft.  of  heating  surface.  Heating  surface  is  defined  as  that 
portion  of  shell,  tubes  and  other  parts  which  is  in  contact  with  the 
gases  of  combustion  on  one  side  and  the  contained  water  on  the 
other. 

QUALITY  OF  STEAM 

Steam  from  practically  all  boilers,  unless  it  passes  through  a 
superheater,  contains  moisture,  that  is,  minute  particles  of  water 
that  has  not  been  changed  from  its  liquid  form  into  the  true 
vaporous  state.  By  innumerable  experiments  it  has  been  proven 
far  beyond  any  doubt  that  when  a  pound  of  water  at  a  certain 
temperature  is  evaporated  into  steam  at  a  certain  pressure  a 
certain  definite  amount  of  heat  is  required.  Now,  then,  if  we 
condense  a  pound  of  what  we  assume  to  be  "pure"  steam  (that  is, 
saturated  steam)  by  injecting  it  into  a  known  weight  of  cool 
water  and  then  carefully  compute  the  heat  it  contained  from  the 
rise  in  temperature  of  the  cooling  water,  we  might  find  that  the 
steam  did  not  contain  all  the  head  that,  according  to  the  steam 
table,  it  should.  In  such  a  case  we  would  know  that  the  steam 
contained  "moisture"  or  was  "wet." 


120       FUEL  ECONOMY  AND  CO2  RECORDERS 

The  reason  why  a  pound  of  wet  steam  does  not  contain  all  the 
heat  it  should  is  because  the  part  that  still  exists  as  liquid  water, 
no  matter  how  fine  or  minute  the  particles  may  be,  has  not  taken 
up  any  latent  heat. 

To  illustrate  with  an  actual  numerical  example,  let  us  assume 
that  we  are  investigating  100  Ib.  of  wet  steam  that  has  been  given 
off  from  a  boiler  at  125  Ib.,  abs.,  pressure.  According  to  the 
steam  table,  a  pound  of  pure  or  dry  saturated  steam  at  125  Ib., 
abs.,  pressure  should  contain  1190.3  B.t.u.  total  heat  above  32 
deg.  F.,  and,  hence,  100  Ib.  should  contain  119,030  B.t.u.  If 
this  100  Ib.  were  injected  into  6000  Ib.  of  water  at  60  deg.,  the 
resultant  weight  of  water  would  be  6100  Ib.  and  the  heat  it  should 
contain  above  32  deg.  would  be  the  119,030  B.t.u.  before  men- 
tioned plus  6000  times  the  degrees  difference  between  3  2  and  60, 
or  168,000  B.t.u.  One  B.t.u.  being  the  quantity  of  heat  required 
to  raise  i  Ib.  of  water  i  deg.,  it  is  evident  that 

6000  X  (60  —  32)  =  168,000  B. t.u. 

would  have  to  be  put  into  the  water  in  raising  it  from  3  2  to  60  deg. 
Thus,  the  total  heat  above  32  deg.  contained  in  the  6100  Ib.  of 
water  should  be 

119,030+  168,000  =  287,030  B.t.u. 

And,  as  the  number  of  degrees  in  temperature  above  32  deg.  must 
be  the  total  heat  contained  in  the  water  divided  by  the  weight  of 
the  water  in  pounds  the  new  temperature  after  the  steam  has  been 
injected  should  be 

32  +  (287,030  -f-  6100)  =  79  deg. 

But,  if  the  thermometer  showed  that  the  actual  temperature 
was  only  78.6  deg.,  and  if  there  had  been  no  radiation  loss,  it 
would  be  evident  that  there  was  a  deficiency  in  the  heat  added  to 
the  water  by  the  steam  of 

(79  —  78.6)  X  6100  =  2440  B.t.u. 

Then,  the  entire  100  Ib.  of  what  we  assumed  was  steam  in  actuality 
must  have  been  only  part  steam  and  part  liquid  water. 


EVAPORATION  121 

Now,  as  the  temperature  of  this  liquid  water  carried  in  the 
steam  is  the  same  as  that  of  the  steam  itself  (if  for  no  other  reason 
than  because  the  steam  and  particles  of  water  arose  together  from 
the  main  body  of  water  in  the  boiler),  it  is  evident  that  the  heat 
of  the  liquid  is  not  deficient,  the  entire  100  Ib.  being  at  the  boiling 
temperature.  Consequently,  the  deficiency  must  all  be  due  to  the 
fact  that  some  of  the  latent  heat  was  not  absorbed.  This  being 
the  case,  the  number  of  pounds  of  water  not  converted  into  steam 
but  simply  floating  in  the  steam  in  small  particles  (thus  contribut- 
ing to  the  weight  of  the  mass  just  the  same  as  though  it  all  were 
steam)  may  be  discovered  by  simply  dividing  the  number  of  lack- 
ing B.tu.  by  the  latent  heat  of  i  Ib.  of  steam  at  the  given  pressure, 
125  Ib.,  abs.,  thus, 

2440  -f-  874.7  =  2.8  Ib. 

Then,  of  the  100  Ib.  of  what  we  assumed  was  steam  only 
100  —  2.8  =  97.2  Ib. 

or  97.2  per  cent,  really  is  steam.  We  say,  consequently,  that  the 
"quality"  of  this  steam  is  97.2  per  cent.,  or  that  the  steam  is 
"97.2  per  cent  dry." 

PRACTICE  PROBLEMS 

A  boiler  is  running  under  120  Ib.,  abs.,  pressure  on  feed  water  at 
160  deg.  What  is  the  factor  of  evaporation? 

If  the  actual  total  evaporation  per  hour  is  8760  Ib.,  what  is  the 
number  of  boiler  horsepower  being  developed? 

SOLUTION  OF  PRACTICE  PROBLEMS 

The  factor  of  evaporation  for  the  conditions  specified  in  the 
problem  may  be  ascertained  by  means  of  the  formula: 

f  =  (g  -  0  +  32 

970.4 


122  FUEL  ECONOMY  AND  CO2  RECORDERS 

By  referring  to  the  steam  table  it  will  be  seen  that  the  total  heat  of 
steam  at  i2o-lb.,  abs., pressure  is  1189.6  B.t.u.  Then  substituting 
in  the  formula,  we  have 

(1189.6  —  160)  +  32       1061.6 
F  =  -  ~  =  1.004 

970:4  970.4 

A  boiler  horsepower  is  equivalent  to  the  evaporation  of  34.5  Ib. 
of  water  per  hour  from  and  at  212  deg.  The  equivalent  evapora- 
tion for  any  set  of  conditions  is  found  by  multiplying  the  actual 
evaporation  by  the  factor  of  evaporation.  Thus,  the  equivalent 
evaporation  for  the  conditions  given  in  the  problem  is 

8670  X  1.094  =  9485  Ib.  per  hr.,. 

and,  hence,  the  number  of  boiler  horsepower  being  developed  is 
9485  ^  34.5  =  275. 

STEAM  CALORIMETERS 

It  is  important  to  know  the  quality  or  the  percentage  of  dryness 
of  steam  when  comparing  boiler  or  engine  tests.  If  this  were  not 
known  and  taken  into  consideration  the  results  of  some  tests 
would  be  misleading. 

Moisture  in  steam  causes  inefficiency  and  when  present  in 
large  quantities  it  is  troublesome  in  the  steam  engine  as  it  makes 
cylinder  lubrication  difficult  and  may  cause  knocking.  It  also 
tends  to  cause  water-hammer  in  the  pipes. 

The  device  used  to  discover  the  percentage  of  moisture  in 
steam  is  called  a  steam  calorimeter.  It  is  not  like  the  fuel  calo- 
rimeter which  is  used  for  estimating  the  heat  value  of  fuels  and 
the  two  should  not  be  confused. 

There  are  three  principal  types  of  steam  calorimeter.  One 
is  the  barrel,  in  which  the  steam  sample  is  injected  into  a  barrel 
of  cool  water  and  the  increase  in  temperature  and  weight  noted, 
from  which  data  the  quality  of  the  steam  can  be  estimated. 
This  type  is  not  popular,  however,  because  very  slight  errors  in 


EVAPORATION  123 

reading  temperatures  and  weights  cause  large  errors  in  the  final 
results. 

Another  type  is  the  separating  calorimeter.  In  this  the 
particles  of  moisture  are  separated  from  the  steam  by  mechanical 
means  in  a  manner  similar  to  that  used  in  an  ordinary  steam 
separator  in  a  pipe  line. 

The  third  type  is  the  throttling  calorimeter,  a  form  of  which  is 
illustrated  on  page  126.  Where  the  percentage  of  moisture  in 
the  steam  does  not  exceed  4  per  cent,  and  where  the  steam  pres- 
sure is  80  Ib.  gage  or  over,  the  throttling  calorimeter  is  very 
accurate  and  convenient,  hence,  its  use  is  preferable.  When 
the  contained  moisture  is  greater  than  4  per  cent,  this  form 
of  calorimeter  is  useless  and  one  of  the  separating  type  must 
be  used. 

As  the  quality  of  the  steam  in  the  great  majority  of  plants 
seldom  falls  below  96  per  cent.,  only  the  throttling  type  of  calo- 
rimeter will  be  taken  up  here.  If  its  principle  and  operation  are 
fully  understood,  no  difficulty  whatever  will  be  experienced  in 
mastering  the  principle  and  operation  of  the  other  types. 

When  steam  in  expanding  forces  the  piston  ahead  in  the 
cylinder  of  an  engine  it  loses  heat,  which  is  spent  in  doing  the  work 
of  making  the  engine  turn  and  running  the  dynamo,  shafting  sys- 
tem or  whatever  the  load-giving  apparatus  happens  to  be.  On 
the  other  hand,  when  steam  is  permitted  to  expand  from  one 
pressure  to  another  without  resistance,  as  it  does  when  flowing 
from  a  hole  in  a  pipe  or  from  a  valve  into  the  open  air,  it  tends 
to  retain  all  the  heat  it  had. 

To  illustrate,  assume  that  a  boiler  is  generating  steam  at  a 
pressure  of  140  Ib.,  abs.,  and  that  this  steam  is  dry  saturated. 
By  referring  to  the  steam  table  it  may  be  ascertained  that  steam  of 
that  pressure  has  a  total  heat  of  1192.2  B.t-u.  per  pound  of  steam. 
If  this  steam  were  allowed  to  flow  through  an  opening  directly 
into  the  atmosphere,  we  would  find  that  the  temperature  of  the 
steam  after  it  emerged  from  the  opening,  and  its  pressure  had 
dropped  to  that  of  the  atmosphere,  was  302.9  deg. — that  is,  if 
we  were  careful  to  avoid  error  due  to  radiation  loss.  The 


124  FUEL  ECONOMY  AND  CO2  RECORDERS 

temperature  of  saturated  steam  at  atmospheric  pressure  is  212 
deg.  Then,  this  steam  must  be  superheated 

302.9  —  212  =  90.9  deg. 

The  total  heat  of  dry  saturated  steam  at  atmospheric  pressure 
is  1150.4  B.tu.  per  pound.  This  superheated  steam  has  all  the 
heat  of  dry  saturated  steam  and  some  more,  as  its  higher  tem- 
perature indicates.  The  specific  heat  of  superheated  steam 
varies  for  different  pressures  and  temperature,  but  for  the  above 
case  would  be  about  0.46.  Hence,  the  excess  heat  must  be 

90.9  X  0.46  =  41.8  B.t.u.  per  pound. 

And  this  value  added  to  the  total  heat  of  dry  saturated  steam  at 
atmospheric  pressure  gives 

1150.4  -f-  41.8  =  1192.2  B.t.u. 

which  is  exactly  the  same  as  the  heat  contained  in  i  Ib.  of  the  steam 
we  started  with,  namely,  dry  saturated  at  140  Ib.,  abs.,  pressure. 

Now,  if  the  i4o-lb.  steam  contained  some  moisture,  the  total 
heat  in  the  mixture  of  steam  and  water  would  be  less  to  begin 
with,  and  the  difference  between  that  heat  and  the  total  heat  of 
steam  at  212  deg.  would  not  all  go  to  superheating  the  steam  at 
atmospheric  pressure,  but  some  of  it  would  be  used  up  in  vaporiz- 
ing the  entrained  moisture  and  the  final  temperature  or  degree  of 
superheat  would,  therefore,  be  considerably  lower  than  above 
shown. 

For  instance,  suppose  the  quality  of  the  steam  were  98  per 
cent,  that  is,  it  contained  2  per  cent,  of  moisture.  The  total 
heat  of  a  pound  of  such  a  mixture  of  steam  and  water  would  be 
the  heat  of  the  liquid  plus  the  latent  heat  of  0.98  Ib.  of  steam, 
or 

324.6  +  (867.6  X  0.98)  =  1174.8. 

Subtracting  from  this,  the  1150.4  B.t.u.,  total  heat  in  i  Ib.  of  dry 
saturated  steam  at  atmospheric  pressure,  we  have 

1174.8  —  1150.4  =  24.4  B.t.u. 


EVAPORATION  125 

excess  heat  instead  of  the  41.8  we  previously  had.    Hence,  the 
degree  of  superheat  would  be 

24.4  -T-  0.46  =  53  deg. 

showing  a  final  temperature,  consequently,  of 
212  +  53  =  265  deg. 

Thus,  by  permitting  steam  to  flow  through  an  opening  into  the 
atmosphere,  observing  the  temperature  change,  and  using  pre- 
caution against  error  due  to  radiation,  we  may  calculate  the  qual- 
ity or  moisture  content  of  such  steam.  A  home-made  form  of  the 
throttling  calorimeter — the  device  used  in  doing  this — is  shown 
in  Fig.  24.  It  can  be  made  of  pipe  and  fittings  as  shown.  Be- 
tween the  flanges  tightly  fit  a  |-in.  steel  plate  with  a  small  orifice 
drilled  through  its  center.  This  orifice  should  not  be  greater 
than  -f%  in.  in  diameter;  ^  in.  would  be  better.  The  thermometer 
wells  can  be  obtained  from  any  instrument  supply  house.  The 
thermometers  should  have  a  range  up  to  400  deg.,  F.,  at  the  very 
lowest.  While  the  calorimeter  can  be  operated  with  fair  success 
with  only  the  lower  thermometer  and  well,  it  is  preferable  to  use 
both  an  upper  and  a  lower;  the  increased  reliability  of  results 
more  than  offsets  the  difference  in  cost. 

When  assembled  and  in  place,  the  calorimeter  should  be  well 
insulated  with  magnesia  or  other  covering  to  eliminate  radiation 
as  much  as  possible  and,  hence,  prevent  error. 

According  to  the  boiler- testing  code  of  the  American  Society 
of  Mechanical  Engineers,  formulated  in  1899,  the  nozzle  A  of  the 
calorimeter  "should  be  placed  in  the  vertical  steam  pipe  rising 
from  the  boiler  *  *  *  and  should  extend  across  the  diameter 
of  the  steam  pipe  to  within  J  in.  of  the  opposite  side  *  *  *  none 
of  these  holes  (in  the  nozzle)  should  be  nearer  than  J  in.  to  the 
inner  side  of  the  steam  pipe." 

Before  any  readings  are  taken  it  is  best  to  let  steam  blow  through 
the  calorimeter  at  full  pressure  for  5  or  10  min.,  so  that  the  entire 
apparatus  will  be  thoroughly  warmed  up  and  error  avoided.  The 


126 


FUEL  ECONOMY  AND  CO2  RECORDERS 


thermometers  should  be  tested  for  accuracy  before  used  and  if  an 
important  variation  is  found  allowance  should  be  made  in  the 
readings.  For  very  accurate  work  corrections  are  made  for  the 


Chemical 
Thermometer 


x.5"  Mercury 
Thermometer 
Well 


c^ia 


FIG.  24. — Construction  of  home-made  steam  calorimeter. 


error  caused  by  the  exposure  of  part  of  the  thermometer  stem  to 
the  room  temperature.     But,  such  connections  are  far  too  small 


EVAPORATION  127 

to  be  of  real  importance  in  every-day  power-plant  test  work. 
So,  they  will  not  be  considered  here. 

When  making  a  test  for  the  quality  of  steam  have  the  valve 
of  the  calorimeter  wide  open  and  read  both  thermometers.  The 
temperature  shown  by  the  upper  thermometer  should  correspond 
very  closely  with  the  temperature  of  steam  at  the  pressure  being 
carried  on  the  boiler.  This  temperature  is  given  in  the  steam 
table.  If  an  appreciable  difference  is  found  this  may  be  taken 
as  an  evidence  that  either  the  steam-pressure  gage  on  the  boiler 
or  the  thermometer  is  inaccurate  and  both  should  be  tested  to 
locate  the  trouble. 

After  the  readings  have  been  taken,  the  quality  of  the  steam 
may  be  estimated  by  the  following  formula,  which  appears  more 
formidable  than  it  really  is. 

(H-h)  +  0.46  (T  -  rp 

y  =  L 

where 

Q  =  Quality  of  steam  expressed  as  a  decimal  fraction; 

H  =  Total  heat  of  dry  saturated  steam  at  atmospheric  pres- 
sure, B.t.u.  per  lb.; 

h  =  Heat   of   the  liquid   corresponding   with   the  pressure 
carried  on  the  boiler,  B.tu.  per  lb.; 

T  =  Temperature    as    shown    by    the   lower    thermometer, 

degrees  F.; 

TI  =  Temperature  of  saturated  steam  at  atmospheric  pressure, 
degrees  F.; 

L  =  Latent  heat  of  steam  at  the  pressure  carried  on  the  boiler, 
B.tu.  per  lb. 

To  illustrate  the  use  of  this  formula,  assume  that  the  boiler 
being  tested  is  at  sea  level  and  that  the  temperature  shown  by 
the  upper  thermometer  is  366  deg.  and  by  the  lower  one,  266  deg. 

Referring  to  the  steam  table,  we  would  find  that  the  steam; 
pressure  corresponding  with  the  temperature  of  366  deg.  is  165 
lb.,  abs.  If  this  figure  checks  up  reasonably  close  with  the  pres- 
sure as  shown  by  the  gage  on  the  boilers,  we  may  proceed  with 


128       FUEL  ECONOMY  AND  CO2  RECORDERS 

our  calculating.  In  making  the  comparison,  don't  forget  to 
subtract  the  atmospheric  pressure  from  the  figure  showing  the 
absolute  pressure,  in  the  present  case,  14.7  Ib. 

All  the  factors,  except  Q  and  T,  are  given  in  the  steam  table; 
T,  given  by  the  lower  thermometer  of  the  calorimeter,  is  266; 
Q  will  be  the  answer.  Substituting, 

(1150.4  -  338.2)  +  0.46  (266  -  212) 
Q=  ~- 


=  0.977 
That  is,  the  quality  of  the  steam  is  97.7  per  cent. 

PRACTICE  PROBLEM 

At  a  plant  considerably  above  sea  level,  the  atmospheric  pres- 
sure is  13  Ib.  per  sq.  in.  A  boiler  was  being  tested  for  the  quality 
of  the  steam  generated.  The  upper  thermometer  of  the  throttling 
calorimeter  used  showed  a  temperature  377.6  deg.,  while  the  lower 
thermometer  showed  286  deg.  The  steam-pressure  gage  on  the 
boiler  indicated  a  pressure  of  177  Ib.,  gage.  What  was  the  quality 
of  the  steam? 


CHAPTER  VIII 
BOILER  EFFICIENCY 

SOLUTION  OF  PRACTICE  PROBLEM 

At  the  plant  in  question  the  atmospheric  pressure  is  13  Ib.  per 
sq.  in.  and  according  to  the  steam  table,  the  total  heat  of 
dry  saturated  steam  at  that  pressure  is  1148  B.t.u.  per  Ib.  and 
its  temperature  is  205.9  deg.  Another  reference  to  the  steam 
table  shows  that  the  absolute  pressure  of  steam  having  a  temp- 
erature of  377.6  deg.  is  190  Ib.  per  sq.  in.,  and  the  heat  of  the 
liquid  of  such  steam  is  350.4  B.t.u.  per  Ib.  while  the  latent  heat 
is  846.9. 

Then,  substituting  in  the  formula  given  (on  page  127)  for  calcu- 
lating the  quality  of  steam  we  have 

=     (1148  -  350-4)  +  0.46  (286  -  205.9)   _ 
^  =  846.9 

797.6  +  (0.46  X  80.1)       797.6  +  36.8 
846.9  846.9 

or  98.52  per  cent,  as  the  quality  of  steam. 

BOILER  EFFICIENCY 

Usually  the  sole  purpose  of  a  steam  boiler  is  to  generate  steam. 
To  do  this,  heat  is  required  and  this  is  obtained  by  burning  fuel 
in  a  furnace  connected  with  the  boiler.  In  reality,  there  are  two 
distinct  steps  in  the  process  of  steam  generation  and  two  parts  in 
the  apparatus  employed.  First,  heat  must  be  generated  and  for 
this  the  furnace  and  grate  when  solid  fuel  is  used  are  required. 
Second,  the  heat  generated  must  be  transferred  to  water  so  as  to 
convert  it  into  steam  and  for  this  the  boiler  proper  is  provided. 
9  129 


130       FUEL  ECONOMY  AND  CO2  RECORDERS 

The  degree  of  perfection  or  the  efficiency  with  which  each  part 
does  its  work  depends  partly  upon  its  design  and  partly  upon  the 
skill  and  care  employed  by  the  operators. 

The  efficiency  of  the  boiler  alone  is  the  ratio  of  the  heat  absorbed 
by  the  water  within  to  the  heat  supplied  to  the  heating  surface. 
To  illustrate,  if  by  calculation  based  upon  the  pounds  of  water 
evaporated  and  the  pounds  of  fuel  actually  burned,  it  were  found 
that  for  every  1000  B.t.u.  actually  liberated  by  the  combustion  of 
the  fuel,  740  is  transferred  to  or  absorbed  by  the  water  in  the  boiler 
to  make  steam,  while  the  balance  was  lost  in  various  ways,  the 
efficiency  of  the  boiler  would  be  as  740  is  to  1000,  or 

740 

X  100  =  74  per  cent. 


1000 

On  the  other  hand,  the  efficiency  of  the  boiler  and  grate,  taken 
as  a  whole,  is  the  ratio  of  the  heat  absorbed  by  the  water  to  the 
total  available  heat  supplied  to  the  furnace,  the  latter  item  being 
based  on  the  number  of  pounds  of  fuel  fired  and  the  heat  value  of 
the  fuel  when  fired. 

The  difference  between  these  two  methods  of  calculating  effi- 
ciency is  that  in  the  first  case  the  boiler  is  not  charged  with  the  loss 
due  to  unburned  fuel  dropping  through  the  grate,  which  is  proper 
as  only  the  grate  and  not  the  boiler  itself  is  responsible  for  loss  in 
this  direction.  Hence,  this  loss  is  taken  into  consideration  only 
when  the  boiler  and  grate  are  all  considered  as  one  unit. 

It  is  customary  to  state  both  efficiencies  when  making  a  report 
of  a  test  but  the  one  of  greater  interest  in  every-day  plant  opera- 
tion is  the  efficiency  of  boiler  and  grate.  In  brief  form  the  two 
efficiencies  are: 

„-  .          f  ,   ..          heat  absorbed  per  Ib.  fuel  burned 
Efficiency  of  boiler  =  -  —f — £—: — 

heat  value  of  i  Ib.fuel 

M  .  heat  absorbed  per  Ib.fuel  fired 

Efficiency  of  boiler  and  grate  = , —    — -= — —f — „    .    , — 

heat  value  of  i  Ib.  fuel 

A  boiler  test  may  be  elaborate  or  simple,  depending  upon  the 
object  in  view.  With  the  elaborate  test  every  factor  possible  is 


BOILER  EFFICIENCY  131 

taken  into  consideration  and  the  greatest  possible  accuracy  is 
secured.  With  the  simple  test  less  effort  is  made  and  fewer  factors 
are  considered.  The  simplest  test  takes  into  consideration  only 
the  weight  of  the  water  apparently  evaporated  and  the  weight  of 
the  fuel  supplied  to  the  furnace.  In  between  come  the  happy 
mediums  which  are  elaborate  enough  to  insure  reasonable 
accuracy  and  simple  enough  to  avoid  expensive  complications  and 
justifiably  dispensable  effort.  Such  a  one  will  be  herein  outlined. 
It  may  be  further  simplified  on  the  judgment  of  the  man  who  is 
conducting  the  test.  All  the  principles  involved  and  all  the  cal- 
culations entering  into  the  making  and  reporting  of  this  test  have 
been  taken  up  in  detail  in  previous  lectures  and  it  only  remains  for 
the  writer  to  show  how  they  all  are  brought  into  application  when 
conducting  a  test. 

TEST  APPARATUS  REQUIRED 

The  following  apparatus  is  required  for  properly  making  a  test 
as  here  outlined: 

1.  Equipment  for  measuring  or  weighing  water  evaporated. 

2.  Equipment  for  measuring  or  weighing  fuel. 

3.  Two  draft  gages;  one  at  damper,  one  at  furnace. 

4.  Four  thermometers;  one  for  feed  water,  one  for  steam  calor- 
imeter, one  for  flue  gases  and  one  for  air. 

5.  One  complete  flue-gas  analyzing  set. 

6.  One  steam  calorimeter. 

7.  One  outfit  for  making  proximate  fuel  analyses. 

WEIGHING  FEED  WATER 

As  probably  has  been  assumed  from  foregoing  paragraphs,  one 
of  the  main  factors  to  be  determined  is  the  weight  of  water  evap- 
orated or  steam  generated  during  the  test.  This  factor  can  be 
ascertained  in  two  ways.  First,  the  water  can  be  measured  or 
weighed  before  it  is  fed  to  the  boiler  or,  second,  the  steam  given  off 
by  the  boiler  can  be  collected,  condensed  and  measured  or  weighed. 


132  FUEL  ECONOMY  AND  CO2  RECORDERS 

The  latter  method  is,  perhaps,  the  more  reliable  because  only 
water  that  has  been  condensed  from  steam  will  be  weighed  while 
with  the  first  method  all  the  water  pumped  into  the  boiler  may 
not  be  evaporated  during  the  test.  If  the  blowoff  should  be  leaky 
some  of  the  water  might  escape  in  that  direction  without  being 
converted  into  steam;  also  the  water  level  in  the  boiler  might  not 
be  the  same  in  the  end  as  in  the  beginning  of  the  test,  thus  causing 
error  in  the  amount  of  work  credited  to  the  boiler. 

It  is  seldom,  if  ever,  possible  to  condense  and  weigh  the  steam 
from  a  boiler  being  tested  because  usually  it  would  be  very  incon- 
venient and  expensive  to  install  a  special  condensing  equipment. 
Besides,  this  method  would  require  taking  the  boiler  out  of 
service  which  sometimes  cannot  be  done.  However,  with  reason- 
able care  the  other  method  gives  practically  as  reliable  results. 

Numerous  methods  of  measuring  or  weighing  the  feed  water  can 
be  devised  and  the  one  best  to  employ  for  any  given  test  depends 
upon  local  conditions,  size  of  the  boiler,  etc.  Ordinarily,  two 
tanks  will  suffice,  one  for  measuring  or  weighing  the  water  as  it  is 
received  from  the  heater  and  one  to  which  the  feed-pump  suction 
is  attached  to  act  as  a  receiving  or  storage  tank.  The  tanks  and 
the  feed  pump  should  be  located  as  close  as  possible  to  the  boiler 
to  be  tested  so  as  to  avoid  radiation  losses.  The  most  convenient 
arrangement  is  to  have  the  measuring  or  weighing  tank  placed 
upon  a  platform  directly  over  the  receiving  tank  so  that  the  dis- 
charge to  the  latter  will  be  as  direct  and  rapid  as  possible.  Prefer- 
ably, the  upper  tank  should  rest  on  a  set  of  scales  so  that  each 
tankful  may  be  actually  weighed.  If  this  is  not  convenient  the 
tank  may  be  provided  with  a  suitable  overflow  and  filled  to  over- 
flowing each  time,  the  capacity  having  first  been  accurately 
determined  by  either  actually  measuring  or  weighing  the 
contents. 

If  possible,  the  thermometer  for  measuring  the  temperature  of 
the  feed  water  should  be  inserted  in  the  feed  pipe  close  to  the  boiler 
by  means  of  a  mercury  thermometer  well.  If  this  cannot  be  done, 
the  thermometer  should  be  hung  in  the  suction  tank. 

For  measuring  the  fuel,  if  it  is  oil,  a  meter  is  usually  employed, 


BOILER  EFFICIENCY  133 

although  a  tank  arrangement  similar  to  that  for  the  feed  water 
could  be  used,  suitable  precautions  being  provided,  of  course, 
against  fire.  If  the  fuel  is  solid,  two  or  more  ordinary  wheel- 
barrows of  suitable  capacity  will  be  required  together  with  a  set  of 
ordinary  platform  scales.  If  the  scales  are  of  the  portable  variety, 
wooden  runs  for  rolling  the  barrows  up  onto  the  platform  and  down 
off  of  it  again  will  be  found  convenient. 

The  two  draft  gages,  specified  as  item  3,  while  not  absolutely 
essential,  will  be  found  instructive  and  helpful  in  analyzing  results. 
One  should  be  connected  with  the  furnace  and  the  other  with  the 
uptake  on  the  boiler  side  of  the  damper.  Any  type  of  gage  will 
suffice,  although  the  more  accurate  it  is  and  the  closer  it  can  be 
read,  the  better. 

The  only  absolutely  necessary  thermometer  specified  in  item 
4  is  that  for  measuring  the  feed-water  temperature.  The  others 
may  be  dispensed  with  if  small  economy  is  any  object.  In  this 
case,  the  steam  calorimeter  would  also  have  to  be  dispensed  with 
and  the  quality  of  the  steam,  and  the  temperature  of  air  and  flue 
gases,  all  of  which  factors  influence  the  results,  would  have  to  be 
guessed  at. 

The  cost  of  the  thermometer  for  the  feed  water  should  not  be 
very  great  as  a  range  up  to  21 2  deg.  will  do,  because  the  feed  water 
must  be  handled  at  atmospheric  pressure  and,  hence,  a  tempera- 
ture higher  than  212  would  be  impossible.  Thermometers  for 
measuring  the  ordinary  atmospheric  temperatures  are  very  cheap. 
Indeed,  they  are  often  given  away  as  advertisements  or  souvenirs, 
consequently,  there  is  little  excuse  for  not  using  one  during  a  test. 
It  should  be  hung  in  such  a  location  that  it  will  indicate  with  fair 
reliability  the  average  temperature  of  the  air  entering  the  boiler 
room. 

The  specifications  and  directions  for  using  the  thermometers  for 
the  flue  gases  and  the  steam  calorimeter  were  given  fully  in  previ- 
ous chapters  and  need  not  be  repeated  here. 

The  function  and  value  of  the  proximate  coal-analysis  outfit, 
flue-gas  analysis  apparatus  and  the  steam  calorimeter  have  also 
been  fully  discussed  in  previous  chapters.  If  a  test  is  an  important 


134  FUEL  ECONOMY  AND  CO2  RECORDERS 

one  it  is  advisable  to  send  a  carefully  collected  sample  of  the  fuel 
to  a  commercial  chemical  laboratory  for  proximate  analysis  and 
heat-value  test  in  order  to  have  a  check  on  your  own  work. 

OBJECT  OF  TEST 

Boiler  tests  may  be  made  for  almost  any  purpose:  To  test  the 
performance  of  a  new  installation;  ascertain  the  efficiency  of  the 
boiler  under  operating  conditions;  determine  the  maximum  capa- 
city that  can  be  developed;  find  the  value  of  a  certain  grade  of 
fuel  or  to  compare  one  grade  with  another;  discover  the  effect  of 
change  in  furnace  design,  type  of  grate  or  stoker,  arrangement  of 
baffles,  etc. 

When  tests  for  comparing  one  set  of  conditions  or  one  kind  of 
fuel  with  another  are  made,  especial  care  should  be  employed  to 
keep  the  operating  conditions  as  uniform  as  possible  so  that  a 
perfectly  fair  comparison  may  be  made.  For  instance,  suppose  a 
new  furnace  is  being  tried  out.  First,  a  test  or  series  of  tests  with 
the  old  furnace  would  probably  be  run  to  discover  the  existing 
economy  and  then  a  test  or  series  with  the  new  equipment  would 
be  conducted  to  discover  what  improvement,  if  any,  had  been 
secured.  Now,  it  would  obviously  be  unfair  to  overhaul  the  boiler 
between  the  first  and  second  tests  or  series,  cleaning  it  thoroughly 
both  outside  and  in  and  carefully  pointing  up  all  cracks  in  the 
setting,  etc.,  and  then  credit  to  the  new  furnace  the  improvement 
in  efficiency  thus  brought  about.  In  the  same  way,  it  would  be 
unfair  to  employ  a  higher  grade  of  skill  in  operation  during  one  set 
of  tests  than  during  the  other,  unless,  of  course,  the  men  of  the 
greater  skill  were  to  operate  the  plant  continuously  in  the  future. 

On  the  other  hand,  if  the  boiler  were  to  be  tested  to  find  out 
just  what  degree  of  efficiency  was  attainable,  it  would  be  poor 
judgment  not  to  take  every  precaution  possible  in  the  way  of 
tuning  up  just  before  the  test. 

Thus,  the  object  or  purpose  of  a  test  should  be  kept  carefully  in 
mind  and  the  method  suitably  adjusted  to  attain  the  desired 
object  as  fairly  and  satisfactorily  as  possible. 

Before  starting  a  test  all  instruments  and  weighing  or  measuring 


BOILER  EFFICIENCY  135 

apparatus  should  be  examined  and  put  in  good  order  and,  where 
deemed  necessary,  they  should  be  tested  for  accuracy.  If  possi- 
ble, the  blowoff  and  other  water  connections  that  can  be  dispensed 
with  temporarily,  such  as  an  extra  feed  pipe,  should  be  discon- 
nected and  sealed  with  blank  flanges.  This  is  to  eliminate  the 
danger  of  error  due  to  water  leaking  out  without  being  evaporated. 
The  boiler  should  be  examined  both  outside  and  in  and  a  full 
memorandum  of  its  condition  during  the  test,  as  indicated  by  this 
preliminary  examination,  should  be  included  in  the  report.  This 
may  be  of  value  in  explaining  why  the  results  secured  are  good, 
bad  or  indifferent,  as  the  case  may  be.  If  the  test  is  for  the  pur- 
pose of  ascertaining  the  highest  obtainable  capacity  or  efficiency, 
the  boiler,  furnace  and  setting  should  be  put  into  the  best  possible 
condition. 

DURATION  OF  TEST 

The  necessary  length  of  the  test  will  depend  on  its  purpose  and, 
somewhat,  on  local  conditions.  The  greater  the  duration  the 
less  will  be  the  effect  of  the  errors  that  occur  at  the  beginning 
and  ending.  Where  the  test  is  run  under  actual  working  condi- 
tions a  duration  of  24  hr.  yields  data  on  all  conditions  of  load  and 
operation.  However,  it  is  not  always  possible  or  convenient  to 
conduct  a  test  of  that  length  and,  hence,  a  shorter  one  is  often 
made  to  suffice.  One  of  8  hr.  is  about  as  short  as  is  safe  if  any 
dependence  is  to  be  put  upon  it;  a  lo-hr.  one  is  better. 

STARTING  AND  STOPPING  TEST 

Unless  proper  care  is  employed  errors  are  likely  to  occur  at  the 
beginning  and  ending  of  a  test.  Effort  should  be  made  to  have 
conditions  at  the  start  and  the  finish  as  nearly  the  same  as  possible; 
the  steam  pressure  and  water  level,  also,  the  size  and  condition 
of  the  fire  should  be  as  nearly  equal  as  possible. 

The  code  of  the  American  Society  of  Mechanical  Engineers 
outlines  two  methods  of  starting  and  stopping.  One  is  called 
the  "standard"  method  and  the  other,  the  "alternate"  method. 
The  first-mentioned  one  consists  of  drawing  the  fire  just  before 


136  FUEL  ECONOMY  AND  CO2  RECORDERS 

the  start  and  building  a  new  one  on  the  clean  grates,  dating  the 
start  from  the  time  a  new  fire  is  lit. 

At  the  end  the  fire  is  burned  thin  and  drawn,  the  finish  being 
dated  at  that  time.  This  method  is  open  to  criticism  as  there  is 
considerable  chance  for  error,  due  to  the  boiler  being  cooled  when 
the  fire  is  drawn  at  the  start  and  finish.  In  addition,  this  method 
is  considerably  less  convenient  than  the  alternate  method.  The 
latter  is  as  follows: 

See  that  the  boiler  has  been  thoroughly  heated  by  a  preliminary 
run  of  suitable  length  at  the  working  pressure.  Burn  the  fire 
low  and  clean  it  well.  Then  make  an  estimate  of  the  thickness 
and  condition  of  the  fire  and  make  a  memorandum  of  this.  Note 
the  time  and  record  this  as  the  starting  time  of  the  test  and  then 
proceed  with  periodic  observation  of  the  various  pressures,  tem- 
peratures, etc.  Stoke  the  fire  with  coal  that  has  been  weighed 
and  keep  a  record  of  the  amount  used.  In  the  same  way,  keep 
a  record  of  the  feed  water  pumped,  starting  with  the  time  that  is 
recorded  as  the  beginning  of  the  test. 

As  soon  as  the  test  is  started,  clean  out  the  ashpit  thoroughly 
and  throw  away  the  ashes  thus  collected  as  they  are  not  to  be 
entered  in  the  test  report.  Before  the  end  of  the  test  the  fire 
should  be  burned  low,  just  as  before  the  start  and  then  cleaned 
so  that  it  will  have  as  nearly  as  possible  the  same  thickness  and 
condition  as  at  the  start.  Likewise,  bring  the  water  level  to  as 
nearly  as  possible  the  same  height  as  at  the  start.  One  way  to 
gage  the  thickness  of  the  fire  is  to  drop  the  rake  into  it  so  that  the 
tines  touch  the  grate  bars  and  then  note  the  distance  they  have 
been  buried  in  the  fuel  bed.  For  convenience  in  keeping  the 
water  level  uniform  a  string  is  tied  around  the  gage-glass  at  the 
level  of  the  water  at  the  start.  With  an  automatic  feed-water 
regulator  this  is  unnecessary  but  still  it  is  a  good  thing  to  have  the 
string  there  simply  as  a  check  on  the  regulator. 

TEST  REPORT 

Table  4  shows  the  standard  form  of  reporting  boiler  tests.  It 
has  been  slightly  changed  and  abbreviated  to  suit  practical  cases 


BOILER  EFFICIENCY  137 

and  filled  in  with  data  from  an  imaginary  test  so  that  it  may  be 
taken  as  a  model  for  regular  use. 

The  number  of  men  required  to  conduct  a  test  depends  upon 
the  number  of  different  observations  to  be  made,  the  interval  of 
time  between  them  and  the  arrangement  of  the  boiler  accessories 
and  testing  apparatus;  hence,  no  definite  directions  can  be  given 
on  this  matter.  If  all  readings  are  taken  every  15  min.,  which  is 
the  customary  interval  when  complete  data  are  desired,  in  addi- 
tion to  one  man  for  measuring  and  recording  the  feed  water  and 
one  man  for  the  coal,  at  least  one  extra  man  will  be  required  to 
analyze  the  flue  gases  and  perhaps  a  fourth  man  will  be  needed  to 
observe  temperatures,  pressures,  etc.  Each  man  should  be  pro- 
vided with  a  suitable  chart  or  paper  which  should,  if  necessary, 
be  ruled  off  so  that  the  time  of  each  reading  as  well  as  the  reading 
itself  may  be  noted  down  without  confusion  and  undue  danger  of 
error.  At  the  end  of  the  test  each  set  of  readings  is  added  up  and 
divided  by  the  total  number  of  times  which  that  particular  reading 
has  been  recorded  so  as  to  get  the  average,  which  is  then  entered 
in  its  proper  place  on  the  report  form.  The  total  coal  and  water 
quantities  are  also  entered  upon  the  report,  as  indicated  in  Table  4. 

In  order  to  present  an  actual  practice  problem  with  which 
those  who  wish  may  test  their  grasp  of  the  subjects  involved, 
only  data  and  not  results  have  been  entered  in  Table  4.  The 
results  and  the  calculations  necessary  to  estimate  them  will  be 
given  in  full  in  the  next  lesson.  The  average  temperature 
shown  by  the  thermometer  on  the  exhaust  side  of  the  calorimeter 
may  be  taken  as  272  deg.,  for  the  imaginary  test. 

TABLE  4.— BOILER-TEST  REPORT  FORM 

Data  and  results  of  evaporative  test 

made  by Arthur  Jones  and  assistants 

Of A  Heine  type  water- tube  boiler 

At Plant  of  Smith  Mfg.  Co.,  New  York  City. 

To  determine Efficiency  under  actual  operating  conditions. 

Kind  of  fuel No.  2  buckwheat 

Kind  of  furnace Hand  fired  with  shaking  grates 

State  of  weather Fair,  with  average  temperature  at  37  deg. 


138  FUEL  ECONOMY  AND  CO2  RECORDERS 

TABLE  4. — Continued 

Method  of  starting  and  stopping Alternate 

Date  of  test Feb.  13,  1913. 

Duration  of  test 10  hr. 

Dimensions  and  Proportions 

Grate  surface Width,  8  ft.  10  in.;  length,  7  ft.;  area,  62  sq.  ft. 

Height  of  furnace 34  in. 

Water-heating  surface 2150  sq.  ft. 

Superheating  surface None 

Average  Pressures 

Steam  pressure  by  gage 103  (abs.)  Ib.  per  sq.  in. 

Draft  at  damper o .  9  in.  of  water 

Draft  in  furnace o .  6  in.  in  water 

Difference  in  draft  between  furnace  and  damper 0.3  in.  of  water 

Difference  in  draft  between  ashpit  and  furnace 0.6  in.  of  water 

Average  Temperature 

Air  in  fire  room 92  deg.  F. 

Feed  water  entering  boiler 199  deg.  F. 

Gases  escaping  from  boiler 540  deg.  F. 

Fuel  • 

Total  weight  of  coal  as  fired 10,372  Ib. 

Moisture  in  coal  as  fired 7  per  cent. 

Total  weight  of  dry  coal  supplied  to  furnace Ib. 

Total  weight  of  ash  and  refuse 1897  Ib. 

Percentage  of  ash  and  refuse  in  dry  coal Ib. 

Proximate  Analysis  of  Coal 

Coal  as 'fired,  Dry  coal,        Combustible, 

per  cent.  per  cent.             per  cent. 

Moisture 7.0  

Volatile  matter 3 . 49  

Fixed  carbon 76 . 35  

Ash 13.16  


Total..  100.  o 


Analysis  of  Ash  and  Refuse 

Combustible  matter per  cent. 

Incombustible  matter per  cent. 


BOILER  EFFICIENCY  139 

TABLE  4. — Continued 

Fuel  per  Hour 

Dry  coal  consumed  per  hour Ib. 

Dry  coal  per  sq.  ft.  grate  per  hour Ib. 

Heat  Value  of  Fuel,  B.t.u.  per  Pound 

Coal  as  Fired         Dry  coal  Combustible 

By  calorimeter 12,600  

Estimated 

Quality  of  Steam 

Moisture  in  steam per  cent. 

Superheat deg. 

Total  weight  of  water  fed  to  boiler 83,125  Ib. 

Water  per  Hour 

Water  fed Ib.  per  hr. 

Water  actually  evaporated  (corrected  for  moisture  in  steam) Ib.  per  hr. 

Factor  of  evaporation 

Actual  equivalent  evaporation Ib.  per  hr. 

Horsepower 

Horsepower  developed 

Builders'  rated  horsepower 220 

Percentage  of  builders'  rating,  developed 

Economic  Results 

Water  apparently  evaporated,  acutual  conditions  per  pound  of  coal  as  fired. Ib. 

Actual  equivalent  evaporation  per  Ib.  coal  as  fired Ib. 

Actual  equivalent  evaporation  per  Ib.  dry  coal  fired Ib. 

Actual  equivalent  evaporation  per  Ib.  combustible  burned Ib. 

Efficiency 

Efficiency  of  boiler  (heat  absorbed  per  Ib.  comb,  burned  divided  by 
heat  value  of  i  Ib.  comb.) per  cent. 

Efficiency  of  boiler  and  grate  (heat  absorbed  per  pound  of  coal  fired 

divided  by  heat  value  of  i  Ib.  coal) per  cent. 

Cost  of  Evaporation 

Cost  of  coal  per  ton  of  2000  Ib.  delivered  in  furnace $2.90 

Cost  of  coal  used  for  evaporating  1000  Ib.  water  from  and  at  212  deg. 


140  FUEL  ECONOMY  AND  CO2  RECORDERS 

TABLE  4. — Continued 

Analysis  of  Flue  Gases 

Carbon  dioxide  (CO2) 10. 7  per  cent. 

Oxygen  (O) 8.7  per  cent. 

Carbon  monoxide  (CO) 0.4  per  cent. 

Nitrogen 

Method  of  Firing 

Kind  of  firing  (spreading,  alternate  or  coking) spreading 

Average  thickness  of  fuel  bed 5  in. 

Average  time  between  firings  for  each  furnace  during  time  when  fires 

are  in  normal  condition u   min. 

Average  time  between  leveling  or  breaking  up 32  min. 

Average  time  between  cleanings 5  hr. 

After  a  test  has  been  conducted  considerable  work  remains  to 
be  done  in  figuring  out  the  results  so  as  to  make  the  report  com- 
plete. While  it  should  be  possible  for  every  reader  to  fill  in  the 
balance  of  the  report  without  further  illustration,  it  seems  desir- 
able to  present  the  calculations  in  full  here  to  serve  as  a  sort  of 
review. 

FUEL 

The  first  item  to  be  calcualted  is  the  total  weight  of  dry  coal 
supplied  to  the  furnace,  which  is  found  by  simply  multiplying  the 
total  weight  of  coal  as  fired  by  100  minus  the  percentage  of  mois- 
ture and  dividing  by  100  thus: 

10.372  X  (ico- 7)  _  lb 

100 

The  percentage  of  ash  and  refuse  in  the  dry  coal  equals  the  total 
weight  of  ash  and  refuse  taken  out  divided  by  the  total  weight  of 
dry  coal  supplied  and  multiplied  by  100,  as  follows: 

~7  X  ioo  =  19.67  per  cent. 
9646 


BOILER  EFFICIENCY  141 

To  calculate  the  proximate  analysis  of  the  dry  coal  from  the 
analysis  of  the  coal  as  fired^add  together  the  percentage  of  volatile 
matter,  fixed  carbon  and  ash,  divide  each  in  turn  by  their  sum  and 
multiply  by  100,  thus: 

3.49  -f  76.35  +  13-16  =  93 
Then,  the  percentage  of  volatile  matter  in  the  dry  coal  is 

-  X  ioo  =  3.75  per  cent. 
the  percentage  of  fixed  carbon  is 

X  ioo  =  82.1  per  cent. 
Vo 

and  the  percentage  of  ash  is 
12.  16 


X  ioo  =  14.15  per  cent. 


The  same  procedure  is  employed  in  calculating  the  analysis  of 
the  combustible  matter,  except  in  this  case  the  percentage  of  ash 
is  also  left  out.  This  analysis  is:  Volatile,  4.37,  and  fixed  carbon, 
95.63  per  cent. 

ANALYSIS  OF  ASH  AND  REFUSE 

An  actual  analysis  of  the  ash  and  refuse  may  be  made  in  the 
same  way  and  with  the  same  apparatus  employed  in  making  the 
proximate  coal  analysis  or  the  analysis  may  be  estimated.  This  is 
done  by  subtracting  the  estimated  total  weight  of  real  ash  from 
the  actual  total  weight  of  ash  and  refuse,  dividing  the  difference 
by  the  latter  and  multiplying  by  ioo.  This  gives  the  percentage 
of  combustible  matter  in  the  ash  and  refuse  and  the  difference 
between  this  figure  and  ioo  gives  the  percentage  of  incombustible 
matter.  The  figures  in  the  present  case  are 

I0'372  X  I3'16  =  I36S  0. 

IOO  °    3 


142  FUEL  ECONOMY  AND  CO2  RECORDERS 

estimated  total  ash  and,  hence, 

1897  -  1365  =  532/6. 
combustible  matter  in  the  ash  and  refuse,  making, 

4r^-  X  100  =  28  per  cent. 
1897 

combustible  matter  in  the  ash  and  refuse  and,  hence, 
100  —  28  =  72  per  cent. 

incombustible  matter. 

The  average  weight  of  dry  coal  consumed  per  hour  is  the  total 
weight  consumed  divided  by  the  number  of  hours,  or, 

9646  -r-  10  =  964.4  Ib. 

and  the  pounds  consumed  per  square  foot  of  grate  per  hour  is  the 
total  weight  consumed  per  hour  divided  by  the  area  of  the  grate 
in  square  feet,  thus: 

964.6  -f-  62  =  15.55  M- 

HEAT  VALUE  or  COAL 

To  estimate  the  heat  value  of  the  dry  coal  the  chart,  Fig.  n 
will  be  required.  The  percentage  of  fixed  carbon  in  the  combusti- 
ble matter  has  just  been  found  to  be  95.63.  Locating  this  point 
on  the  bottom  of  the  chart  and  tracing  a  vertical  line  up  to  the 
curve,  then  across  to  the  left  margin  shows  that  the  heat  value  of 
the  combustible  should  be  about  14,900  B.t.u.  per  Ib.  As  the 
combustible  matter  composes  but  85.85  per  cent,  of  the  dry  coal, 
the  heat  value  of  i  Ib.  of  dry  coal  will  be  but  85.85  per  cent,  of 
that  of  i  Ib.  of  combustible,  or, 

14,900  X  85.85  = 

100 

and,  as  the  combustible  matter  in  i  Ib.  of  coal  as  fired  equals  only 
79.84  per  cent.,  the  heat  value  of  i  Ib.  of  coal  as  fired  is  only 

X  79-84 
ioo 


BOILER  EFFICIENCY  143 

To  estimate  the  heat  value  of  the  combustible  from  the  heat 
value  of  the  dry  coal  as  shown  by  the  calorimeter  test  it  is  simply 
necessary  to  invert  the  latter  part  of  the  above  process.  The 
12,600  B.t.u.  shown  by  the  calorimeter  to  be  the  heat  value  of  i 
Ib.  of  dry  coal  is  really  the  heat  value  of  the  0.8585  Ib.  of  combus- 
tible contained  in  a  pound  of  coal.  Hence,  the  heat  value  of  one 
whole  pound  of  combustible  must  be 

12,600  -r-  0.8585  =  14,677  B.t.u. 

The  heat  value  of  the  coal  as  fired  is  figured  from  the  heat  value 
of  the  dry  coal,  as  shown  by  the  calorimeter  in  exactly  the  same 
manner  as  in  the  case  of  the  estimated  values  just  illustrated. 
Thus,  the  heat  value  of  the  coal  as  fired  is 

".600X93  8  ^^ 

100  "  * 


MOISTURE  IN  STEAM 
The  quality  of  the  steam  may  be  estimated  by  the  formula: 


For  the  conditions  of  the  test  H,  the  total  heat  of  dry-saturated 
steam  at  atmospheric  pressure,  equals  1150.4  B.t.u.  per  Ib.;  h, 
the  heat  of  the  liquid  corresponding  with  the  pressure  carried  in 
the  boiler,  equals  300.6  B.t.u.  per  Ib.;  T,  the  temperature  on  the 
discharge  side  of  the  steam  calorimeter,  equals  272  deg.  F.;  T\t 
temperature  of  saturated  steam  at  atmospheric  pressure,  equals 
212  deg.,  andL,  the  latent  heat  of  steam  at  the  boiler  pressure, 
equals  886.3  B.t.u.  per  Ib.  Substituting  these  values  in  the  for- 
mula we  have 

(1150.4-300.6)  +0.46  (272  -  212) 
^=  886.3 

849.8  +  27.6 


144  FUEL  ECONOMY  AND  CO2  RECORDERS 

or  99  per  cent.,  which  means  that  there  was 
100  —  99  =  i  per  cent. 

of  moisture  in  the  steam. 

The  water  fed  to  the  boiler  per  hour  is  the  total  water  fed 
divided  by  the  number  of  hours,  thus: 

83,  125  -f-  10  =  8312.5  Ib. 

The  water  actually  evaporated  per  hour  is  the  water  fed  per 
hour  multiplied  by  the  quality  of  the  steam  expressed  as  a  decimal 
fraction,  or, 

8312.5  X  0.99  =  8229.4  Ib. 

The  formula  of  calculating  the  factor  of  evaporation,  is 


970.4 

For  the  conditions  of  the  test  H,  the  total  heat  above  32  deg.  in 
the  steam  at  boiler  pressure,  equals  1186.9  B.t.u.  per  Ib.,  and  /, 
the  temperature  of  the  feed  water,  is  099  deg.  Substituting  in 
the  formula,  we  have 

p  =  (1186.9  -199)  +  32  = 
970.4 

The  actual  equivalent  evaporation  per  hour  is  the  actual 
evaporation  per  hour  multiplied  by  the  factor  of  evaporation,  thus: 

8229.4  X  1.051  =  8649  to* 

The  horsepower  developed  is  the  average  actual  equivalent 
evaporation  per  hour  divided  by  34.5;  hence,  the  horsepower 
developed  in  the  present  test  was 

8649-^-34.5  =  250.7 
The  percentage  of  builders'  rating  developed  is  found  by  divid- 


BOILER  EFFICIENCY  145 

ing  the  horsepower  actually  developed  by  the  builders'  rating  and 
multiplying  by  100,  thus: 

250.7 

-  X  ioo  =  114  per  cent. 

The  water  apparently  evaporated  per  pound  of  coal  as  fired 
under  actual  conditions  equals  the  water  actually  fed  per  hour 
divided  by  the  weight  of  coal  per  hour  as  fired,  or, 

8312.5  -T-  1037.2  =  8.01  Ib. 

The  actual  equivalent  evaporation  per  pound  of  coal  as  fired 
equals  the  above  figure  multiplied  by  the  quality  of  the  steam 
(expressed  as  a  fraction)  and  the  factor  of  evaporation,  thus: 

8.01  X  0.99  X  1.051  =  8.33  Ib. 

The  actual  equivalent  evaporation  per  pound  of  dry  coal  fired 
equals  the  actual  equivalent  evaporation  per  hour  divided  by  the 
number  of  pounds  of  dry  coal  supplied  per  hour,  or, 

8649  ~*~  964.6  =  8.97  Ib. 

In  estimating  the  analysis  of  the  ash  and  refuse  we  found  that 
a  total  of  532  Ib.  or  53.2  Ib.  of  combustible  matter  fell  through 
the  grate  to  the  ashpit. 

The  dry  coal  fired  per  hour  weighed  964.6  Ib.  and  of  this 
85.85  per  cent,  or  828.1  Ib.,  was  combustible  matter.  Hence, 
the  percentage  of  combustible  matter  falling  to  the  ashpit  was 

t  X  ioo  =  6.42  per  cent. 


As  the  combustible  matter  comprised  85.85  per  cent,  of  the  dry 
coal  and  as  ah1  the  heat  was  furnished  by  the  combustible  matter, 
it  is  evident  that  the  8.97  Ib.  actual  equivalent  evaporation  per 
pound  of  dry  coal  fired  was  really  8.97  Ib.  actual  equivalent 
evaporation  per  0.8585  Ib.  combustible  matter  fired.  Hence, 


146       FUEL  ECONOMY  AND  CO2  RECORDERS 

the  actual  equivalent  evaporation  per  pound  of  combustible  fired 
must  be 


But,  6.42  per  cent,  of  the  combustible  fired  fell  into  the  ashpit, 
was  unburned  and,  hence,  supplied  no  heat.  Therefore,  the 
10.45  Mb.  actual  equivalent  evaporation  per  pound  of  combustible 
fired  is  10.45  Ib.  per 

100  —  6.45 
-J^J  =  °-93SS  ». 

of  combustible  burned,  or 

10.45-^-0.9355  =  11.17  #• 

per  pound  of  combustible  burned. 

The  heat  absorbed  per  pound  of  combustible  burned  equals 
the  number  of  pounds  of  actual  equivalent  evaporation  per  pound 
of  combustible  burned  multiplied  by  the  latent  heat  of  steam  at 
atmospheric  pressure,  or  970.4.  Then,  in  the  present  case  the 
heat  absorbed  equals 

11.17  X  97°-4  =  I0fi39  B-t.u. 

and,  as  the  heat  value  of  a  pound  of  combustible  was  found  to  be 
14,677  B.t.u.,  the  efficiency  of  the  boiler  is 

X  ico  =  73.58  per  cent. 
14,677 

In  a  similar  way  the  efficiency  of  the  boiler  and  grate  equals  the 
actual  equivalent  evaporation  per  pound  of  coal  fired,  multiplied 
by  970.4  and  divided  by  the  heat  value  of  i  Ib.  of  coal  and  all 
multiplied  by  100,  thus: 


I  2,OOO 

If  the  actual  equivalent  evaporation  per  pound  of  coal  as  fired 


BOILER  EFFICIENCY  147 

was  8.33  lb.,  the  number  of  pounds  of  coal  as  fired  required  to 
evaporate  1000  lb.  of  water  jfrom  and  at  212  deg.  was 


-f-  8.33  =  120 
and  as  this  quantity  is 

1  20 

-  X  100  =  6  per  cent. 
2  coo 

of  one  ton,  the  cost  of  evaporating  1000  lb.  of  water  was 

2-90x6 


CHAPTER  IX 
HEAT  BALANCE 

In  preceding  chapters  a  method  was  given  for  conducting  a 
boiler  test,  making  and  estimating  the  efficiency  and  economic 
results.  After  a  test  has  been  made  the  owner  or  engineer  may  be 
dissatisfied  with  the  showing  made.  He  may  have  been  justified 
in  expecting  a  better  efficiency  when  the  design,  arrangement  and 
condition  of  the  boiler,  furnace  setting,  etc.,  are  taken  into  consid- 
eration. The  test  report  alone  does  not  show  him  in  what  particu- 
lar the  operation  was  poor,  it  simply  gives  final  results.  To  get 
fuller  information  as  to  how  the  operation  can  be  improved  it  is 
necessary  to  analyze  the  distribution  of  the  heat  contained  in  the 
coal.  Perhaps  in  every  pound  of  coal  thrown  into  the  furnace 
there  was  14,000  B.t.u.  available.  If  all  this  heat  could  be  put  into 
the  water,  an  efficiency  of  100  per  cent,  would  be  obtainable. 

Unfortunately,  this  is  impossible — some  loss  is  bound  to  take 
place.  At  the  very  beginning,  some  of  the  burnable  matter  falls 
through  the  grate  with  the  ash.  Hence,  all  the  combustible  mat- 
ter of  the  original  pound  of  coal  is  not  burned  and,  consequently, 
the  full  14,000  B.t.u.  is  not  generated.  Next,  the  moisture  in  the 
coal  must  be  evaporated  and  superheated  and  all  the  heat  that 
such  moisture  carries  out  with  the  flue  gases  is  lost. 

The  air  fed  into  the  furnace  all  passes  out  again  to  the  chimney. 
True,  a  part  of  it  has  undergone  a  change  (the  oxygen  combining 
with  the  hydrogen  and  carbon  of  the  fuel)  but  it  is  all  there  never- 
theless. This  air  leaves  the  boiler  at  a  considerably  higher  tem- 
perature than  that  at  which  it  entered.  The  heat  added  to  it  was 
obtained  from  the  coal — and  nowhere  else.  Hence,  here  is  another 
loss.  And  so  it  goes;  some  heat  radiates  from  the  boiler  and  set- 
ting, and  some  more  heat  is  lost  through  the  incomplete  combus- 

148 


HEAT  BALANCE  149 

tion  of  the  carbon  in  the  fuel.  Some  heat  is  lost  through  unburned 
particles  of  combustible  matter  passing  up  the  stack  as  soot,  and 
some  is  lost  because  all  the  heat  created  by  the  combustion  of  the 
hydrogen  in  the  fuel  cannot  be  recovered  in  the  boiler. 

An  itemized  statement  in  B.t.u.  and  percentage  of  all  these 
losses  together  with  the  quantity  of  heat  absorbed  by  the  water  in 
the  boiler  to  make  steam  is  called  a  heat  balance.  To  itemize  each 
loss  individually  would  necessitate  considerable  trouble  in  the  way 
of  obtaining  the  required  data  so  only  six  divisions  are  usually 
made: 

(a)  Loss  due  to  moisture  and  hydrogen  in  coal. 

(b)  Loss  due  to  heat  carried  away  by  dry  flue  gases. 

(c)  Loss  due  to  incomplete  combustion. 

(d)  Loss  due  to  coal  dropping  through  grates. 

(e)  Heat  unaccounted  for  (this  item  includes  all  losses  not 
taken  into  consideration  in  the  four  foregoing  items). 

(f)  Heat  put  into  the  water. 

Item  (a)  is  made  up  of  two  factors:  r,  the  loss  of  heat  required 
to  change  the  moisture  in  the  coal  into  steam  at  the  temperature 
of  the  gases  leaving  the  boiler  and,  2,  the  loss  due  to  the  fact  that 
all  of  the  heat  generated  by  the  combustion  of  the  hydrogen  of  the 
fuel  cannot  be  used  for  making  steam  in  the  boiler.  When  hydro- 
gen burns  it  forms  water  in  the  shape  of  highly  superheated  steam 
which  in  the  fuel  calorimeter  is  condensed  so  that  the  latent  heat 
of  this  steam  passes  into  the  cooling  water  surrounding  the  bomb 
and  is  credited  to  the  coal.  In  actual  use  in  the  boiler,  however, 
the  steam  formed  by  the  combustion  of  the  hydrogen  is  partly 
cooled  by  contact  with  the  heating  surface  of  the  boiler,  but  it  is 
not  cooled  sufficiently  to  condense  and,  consequently,  it  passes  off 
in  a  superheated  condition  at  the  temperature  of  the  chimney 
gases.  Hence,  the  additional  heat  it  would  give  up  if  cooled  down 
to  ordinary  temperatures  and  condensed  is  lost. 

The  heat  given  up  when  a  pound  of  superheated  steam  at  atmos- 
pheric pressure  is  condensed  and  cooled  from  500  deg.  to  70  deg.  is 
exactly  equal  to  the  heat  required  to  evaporate  and  superheat  a 
pound  of  water  from  70  to  500  deg.  Hence,  for  simplicity  and 


150  FUEL  ECONOMY  AND  CO2  RECORDERS 

convenience  it  is  customary  to  calculate  the  amount  of  water  that 
would  be  formed  from  the  estimated  quantity  of  hydrogen  in  the 
coal  and  add  this  to  the  amount  of  moisture  in  the  coal  as  shown  by 
the  proximate  analysis  and  then  calculate  the  heat  required  to 
raise  the  total  quantity  to  the  boiling  point,  convert  it  into  steam 
and  superheat  it  to  the  temperature  of  the  escaping  gases. 

The  first  step,  then,  is  to  estimate  the  percentage  of  hydrogen 
in  the  coal,  for  it  is  seldom  that  an  ultimate  analysis  is  avail- 
able in  commercial  practice.  The  following  formula,  originated 
by  Professor  Diederichs,  gives  the  approximate  total  hydrogen 
in  the  combustible  matter: 


where 

H  —  percentage  by  weight  of  hydrogen  in  the  combustible 

matter; 
•o  =  percentage  by  weight  of  volatile  matter  in  the  combust- 

ible matter. 

For  illustrating  the  application  of  this  formula  and  other  cal- 
culations required  in  constructing  a  heat  balance  the  data  and 
results  of  the  imaginary  test  reported  in  a  previous  chapter  will 
be  used.  In  the  calculations  in  the  last  chapter  it  was  found  that 
the  percentage  of  volatile  matter  in  the  combustible  was  4.37. 
Substituting  in  the  foregoing  formula  we  have 


a  =  4.37  ~TO  -  0-013 

hydrogen  in  the  combustible  matter.     As   there  is  only  79.84 
per  cent.,  or  0.7984  Ib.  combustible  in  each  pound  of  coal  as  fired, 
the  percentage  of  hydrogen  in  the  coal  as  fired  is  only 
(2.18  X  79.84)  -T-  100  =  1.74  per  cent. 
or  0.0174  Ib.  hydrogen  per  pound  of  coal  as  fired. 

It  was  shown  that  the  combustion  of  every  pound  of  hydrogen 
results  in  the  production  of  9  Ib.  of  water.     Consequently,  the 
combustion  of  0.0174  Ib.  of  hydrogen  results  in  the  production  of 
0.0174  X  9  =  0.157  ^- 


HEAT  BALANCE  151 

The  proximate  analysis  of  the  coal  used  in  the  test  showed  that 
in  each  pound  of  coal  as  fired  there  was  0.07  Ib.  of  water.  Then, 
the  loss  due  to  the  hydrogen  and  moisture  in  the  coal  as  fired  is 
equal  to  the  heat  required  to  evaporate  and  superheat 

0.157  "H  °-°7  =  0.227  Ib. 

of  water  from  92  to  540  deg.,  the  temperatures  given  in  the  test 
report. 

The  heat  required  to  raise  this  quantity  of  water  from  92  deg. 
to  the  boiling  point,  212  deg.,  is 

(212  —  92)  X  0.227  =  27.24  B.t.u. 

The  heat  required  to  change  this  water  into  steam  from  and  at 
212  deg.  (latent  heat)  is 

970.4  X  0.227  =  220.28  B.t.u. 

And,  assuming  the  specific  heat  of  superheated  steam  to  average 
0.46,  the  heat  required  to  superheat  the  steam  from  212  to  540 
deg.  is 

(540  —  212)  X  0.227  X  0.46  =  34.25  B.t.u. 
Hence,  the  total  loss  per  pound  of  coal  as  fired,  due  to  the  hydrogen 
and  moisture,  is 

27.24  +  220.28  +  34.25  =  282  B.t.u. 

As  the  heat  value  of  the  coal  as  fired  was  11,718  B.t.u.  per  Ib. 
this  loss  expressed  in  percentage  is 

(282  -r-  11,718)  X  ioo  =  2.4  per  cent. 

In  the  present  case  this  loss  is  not  very  high,  because  the  coal 
used  was  of  the  anthracite  grade  in  which  the  percentage  of  mois- 
ture and  hydrogen  never  runs  very  high.  But,  with  other  grades, 
especially  the  bituminous  and  lignite,  the  loss  runs  considerably 
higher. 

Item  (b)  of  the  heat  balance  is  the  most  important  because  it 
is  the  largest  and  its  magnitude  depends  greatly  upon  the  skill 
and  care  used  in  operation. 

A  formula  for  estimating  the  heat  lost  up  the  chimney  per  pound 
of  coal  burned  is: 

L  =  0.24    W  CT-t) 


152  FUEL  ECONOMY  AND  CO2  RECORDERS 

where, 

L    =  B.t.u.  lost  up  the  chimney  per  pound  of  fuel  burned; 

W  =  weight  of  flue  gas  formed  per  pound  of  fuel  burned; 

T  =  temperature  of  the  gases  leaving  the  boiler; 
/  =  temperature  of  the  air  entering  the  furnace. 

The  weight  of  the  flue  gases  formed  per  pound  of  coal  burned 
is  estimated  by  another  formula  as  follows: 


where 

C  =  weight  of  total  carbon  in  the  fuel  as  fired; 
N,  CO*  and  CO  =  percentage  by  volume   of   nitrogen,    carbon 
dioxide  and  carbon  monoxide,  respectively, 
in  the  flue  gases; 

A  =  weight  of  ash  in  the  fuel  as  fired. 

When  the  volatile  matter  in  the  combustible  amounts  to  12 
per  cent,  or  more  the  total  carbon  in  the  coal  as  fired  is  found 
with  the  aid  of  the  chart,  Fig.  n.  Where  it  runs  Jess,  it  is  safe 
enough  to  assume  that  the  volatile  carbon  is  approximately  one- 
third  of  the  volatile  matter.  Thus,  in  the  present  case,  the  vola- 
tile carbon  in  the  coal  as  fired  would  be 

3.49  -T-  3  =  1.16  per  cent. 
and  the  total  carbon  would  be,  therefore, 

76.35  -f  1.16  =  77.51  per  cent. 

or  0.7751  Ib.  per  Ib.  of  coal  as  fired.  Substituting  in  the  foregoing 
formula  this  value  and  the  values  for  the  flue  gases  as  given  in  the 
test  report  we  have: 


w  =  3.032  x  0-7751  i       +  a  -  0.1316)  =  17.85  w. 

And  applying  this  factor  in  the  formula  for  heat  loss  we  have 

L  =  0.24  X  17.86  (540  —  92)  =  1920  B.t.u. 
per  pound  of  coal  burned,  carried  up  the  chimney  by  the  flue 
gases.    Expressed  in  percentage  this  equals 

(1920  +  11,718)  X  100  =  16.38  per  cent. 


HEAT  BALANCE  153 

The  method  of  calculating  item  (c)  was  given  in   Chapter 
VIII.     The  formula  is, 


in  which  L'  equals  the  heat  loss  due  to  incomplete  combustion 
per  pound  of  coal  burned  and  expressed  in  B.tu.,  and  the  other 
symbols  represent  the  same  values  as  before.  The  heat  loss  in 
the  present  case  is 

L'  =  io,i5o(-  —  (0.7751  =  283  B.t.u. 

\o.4  +  10.77 

or 

(283  -r-  11,718)  X  ioo  =  2.41  per  cent. 

In  the  last  chapter  it  was  estimated  that  there  was  532  Ib.  of 
combustible  matter  in  the  ash  and  refuse.  As  the  heat  value  of 
the  combustible  was  found  to  be  14,677  B.t.u.  per  Ib.,  the  total 
heat  loss  due  to  unburned  coal  dropping  through  the  grates  was 

14,677  X  532  =  7,808,164  B.t.u. 

And,  consequently,  the  loss  per  pound  of  coal  fired  (item  (d)  of 
the  heat  balance)  was 

7,808,164  -4-  10,372  =  753  B.t.u. 
which,  expressed  in  percentage  equals, 

(753  -T-  11,718)  X  ioo  =  6.43  per  cent. 

Item  (e)  is  the  difference  between  the  heat  value  of  the  coal  as 
fired  and  the  sum  of  all  the  other  items. 

The  efficiency  of  the  boiler  and  grate  was  found  to  be  68.98 
per  cent.  In  other  words, 

(11,718  X  68.98)  -f-  ioo  =  8083  B.t.u. 

was  put  into  the  water  in  the  boiler  to  make  steam.    Then,  item 

(e),  representing  all  other  losses  or  losses  unaccounted  for  must  be, 

11,718  -  (282  +  1920  +  283  +  753  +  8080)  =  397  B.t.u. 

(397  -T-  11,718)  X  ioo  =  3.39  per  cent. 

All  the  items  of  a  heat  balance  are  usually  arranged  in  tabular 
form,  thus: 


154  FUEL  ECONOMY  AND  CO2  RECORDERS 

HEAT  BALANCE 
Heat  value  of  i  Ib.  coal  as  fired  =  11,718  B.t.u. 

Distribution  of  heat                                  B.t.u.  Per  cent, 

(a)  Loss  due  to  moisture  and  hydrogen  in  coal 282  2 .41 

(b)  Heat  carried  away  by  flue  gases 1,920  16 .38 

(c)  Loss  due  to  incomplete  combustion 283  2 .41 

(d)  Loss  due  to  unburned  coal  dropping  through  grates          753  6.43 

(e)  Losses  unaccounted  for 397  3 . 39 

(f)  Heat  absorbed  by  boiler 8,080  68.98 

Total 11,718    •    100.00 


CHAPTER  X 
FEED-WATER  TREATMENT 

A  cardinal  requisite  to  high  boiler  efficiency  and  consequent 
low  operating  cost  is  a  clean  boiler  both  outside  and  in.  The  man 
who  neglects  to  protect  the  outside  of  the  heating  surface  from  the 
accumulation  of  slag,  soot,  etc.,  and  the  inside  from  accumulation 
of  scale,  etc.,  simply  because  it  is  a  bother  to  do  so,  is  not  living  up 
to  his  opportunities. 

The  main  sources  of  feed- water  supply  are  wells,  rivers,  ponds, 
lakes,  etc.  The  great  primary  sources  of  supply  to  these  second- 
ary sources  are  the  oceans  which  cover  about  three-quarters  of  the 
earth's  surface.  This  water  contains  so  much  impurities  that  it  is 
unfit  to  drink  or  to  use  in  a  boiler  until  it  is  purified.  The  chief 
impurity  is  salt,  the  chemical  name  of  which  is  sodium  chloride 
and  the  chemical  symbol  is  NaCl.  The  letter  S  could  not  be  used 
in  the  symbol  because  S,  you  will  remember,  is  the  symbol  for 
sulphur,  so  the  abbreviation  Na,  of  the  Latin  name  natrium,  is 
employed. 

A  gallon  of  sea  water  contains  about  1.75  Ib.  of  salt.  To 
illustrate  how  difficult  it  would  be  to  operate  on  sea  water,  it  has 
been  estimated  that  a  72-in.  by  i8-ft.  tubular  boiler  (150  hp.), 
if  it  could  be  operated  continuously  at  its  rated  capacity  on  sea 
water,  would  fill  solid  to  the  water  line  with  salt  in  about  48  hr. 

For  stationary  boiler  plants,  nature  herself  performs  part  of  the 
purifying  process.  The  heat  of  the  sun  causes  ocean  water  to 
evaporate  and  rise  in  the  atmosphere  to  form  clouds.  As  salt 
does  not  vaporize  at  ordinary  temperatures  it  remains  behind, 
while  only  the  pure  water  itself  rises  in  the  air.  Changes  in  the 
atmospheric  temperature  and  pressure  cause  the  vapor  to  condense 
to  the  liquid  form  again  and  fall  to  earth  as  rain.  Rain  water  is 
almost  absolutely  pure. 


156  FUEL  ECONOMY  AND  CO2  RECORDERS 

Water  has  great  powers  for  dissolving  substances.  Almost 
everything  in  the  world  can  be  dissolved  in  it.  Some  substances 
dissolve  very  slowly  and  only  in  exceedingly  minute  quantities 
while  others  dissolve  very  quickly  and  in  large  quantities.  In 
sinking  into  the  ground  or  running  off  to  the  river  or  lake,  the  pure 
rain  water  dissolves  substances  that  it  happens  to  meet,  thus 
becoming  impure.  The  quantity  of  any  given  substance  which 
the  water  will  dissolve  and  carry  along  with  it  depends  upon  the 
readiness  with  which  the  substance  dissolves  and  the  length  of 
time  the  water  is  in  contact  with  it. 

Of  the  many  substances  that  may  exist  in  a  dissolved  state  in 
water,  we  are  interested  in  only  those  which  tend  to  cause  scale, 
sediment  and  corrosion.  These  in  themselves  are  quite  numerous 
and  a  full  study  of  and  treatment  for  them  all  can  be  made  only 
by  a  trained  chemist.  Hence,  when  a  feed  water  is  causing  trouble 
it  is  very  often  advisable  to  submit  a  sample  to  a  competent  and 
reliable  chemist  or  company  for  analysis  and  prescription  or  treat- 
ment. However,  as  there  are  a  few  impurities  which  cause  the 
greater  part  of  the  trouble  encountered,  a  short  study  of  these, 
including  an  explanation  of  their  action,  how  they  are  detected, 
their  quantity  estimated  and  a  neutralization  or  elimination 
effected,  may  be  worth  while. 

COMMON  IMPURITIES 

The  commonest  impurities  found  in  water  are  calcium  carbon- 
ate, magnesium  carbonate,  calcium  sulphate  and  magnesium 
sulphate — rather  formidable  names  but  really  not  such  formidable 
substances,  because  all  four  of  them  possess  only  two  elements 
that  can  possibly  be  new  or  strange  to  the  students  of  this 
course. 

CALCIUM  CARBONATE 

The  chemical  formula  for  calcium  carbonate  is  CaCOa.  This 
means  that  it  is  composed  of  one  combining  weight  of  calcium, 


FEED-WATER  TREATMENT  157 

one  of  carbon  and  three  of  oxygen.  The  calcium  is  the  only  ele- 
ment that  is  new  to  us.  It  is  a  metal  but  one  which  is  never  found 
in  its  pure  or  uncombined  state  in  nature  because  it  is  a  very 
active  element  and  readily  forms  compounds  with  other  elements. 
Its  compounds,  however,  are  very  common  substances.  One  of 
its  most  familiar  and  useful  compounds  is  ordinary  lime,  such  as 
used  for  making  mortar  and  plaster.  The  chemical  formula  for 
this  substance  is  CaO  and  its  chemical  name  is  calcium  oxide. 
When  water  is  added  to  lime,  making  slack  lime,  the  formula  is 

CaO  +  H2O  =  CaO2H2 

Pure  calcium  can  be  produced  artificially  by  reducing  one  of  its 
compounds.  When  pure  and  fresh  a  piece  of  it  looks  like  zinc. 
But  when  exposed  to  the  air  a  while  it  becomes  yellowish  and  fi- 
nally gray  or  white  in  color,  due  to  a  reaction  between  it  and  the 
oxygen  and  moisture  of  the  air  resulting  in  a  layer  of  slaked  lime 
(CaO2H2).  The  combining  weight  of  calcium  is  40.1  and,  it  will 
be  remembered,  the  combining  weights  of  carbon  and  oxygen  are 
12  and  16,  respectively.  Then,  as  its  formula  indicates,  calcium 
carbonate  is  composed  of  these  three  elements  in  proportion  of 
40.1  Ib.  of  calcium,  12  Ib.  of  carbon  and  3  X  16  =  48  Ib.  of  oxy- 
gen. Chalk,  limestone  and  marble  are  all  almost  pure  calcium 
carbonate. 

Pure  water  is  capable  of  dissolving  calcium  carbonate  in  very 
small  quantities — 10,000  parts  of  water  are  required  to  dissolve 
one  part  of  calcium  carbonate.  That  is,  to  dissolve  i  Ib.  of  chalk 
would  require  10,000  Ib.  of  water  or  some  1200  gal.  and  a  peculiar 
fact  is  that  calcium  carbonate  is  less  soluble  in  hot  water  than  in 
cold.  If  this  was  the  only  rate  at  which  calcium  carbonate  could 
get  into  a  boiler  (i  Ib.  per  10,000  of  water)  there  would  not  be  much 
difficulty  in  coping  with  it.  But  it  is  not.  Carbonic  acid  or 
carbon  dioxide  (CO2),  our  old  friend  which  is  formed  when  carbon 
is  burned,  can  be  absorbed  by  or  dissolved  in  water,  and  in  its 
descent  through  the  air  and  travels  on  and  in  the  earth  water  does 
absorb  some  of  this  gas.  Now,  when  water  containing  carbon 
dioxide  flows  over  chalk,  limestone,  rocks,  marble  or  other  sub- 


158  FUEL  ECONOMY  AND  CO2  RECORDERS 

stances  mainly  composed  of  calcium  carbonate,  the  carbon  diox- 
ide, water  and  calcium  carbonate  all  get  together  and  form  a  sub- 
stance known  as  calcium  bicarbonate — CaH^COs^ — a  substance 
which  water  can  dissolve  and  carry  in  solution  in  quite  large 
quantities. 

This  calcium  bicarbonate,  however,  is  not  a  very  stable  com- 
pound. When  the  water  containing  it  is  heated  to  180  deg.  F. 
or  more,  it  begins  to  break  up  into  its  three  components — CO2, 
water,  and  calcium  carbonate.  The  COz  now  changes  (due  to  the 
heating  of  the  water)  into  its  gaseous  form  and,  rising  through  the 
water  in  bubbles,  escapes  in  the  atmosphere.  This  leaves  an 
excess  of  calcium  carbonate  in  the  water,  which,  as  was  just  stated, 
is  only  slightly  soluble  in  water.  This  excess,  therefore,  settles 
to  the  bottom  as  a  fine  powder. 

When  a  substance  is  suddenly  changed  to  its  solid  form  and 
settles  out  of  the  liquid  in  which  it  was  dissolved  (as  in  the  case 
just  described)  it  is  said  to  have  been  "precipitated"  or  "thrown 
down"  and  the  process  is  called  precipitation. 

The  foregoing  paragraphs  show  why  some  boilers  are  found  to 
contain  internal  coatings  of  soft  sand-like  or  mud-like  material. 
They  have  been  fed  with  water  carrying  calcium  bicarbonate 
which  the  heat  has  changed  back  to  calcium  carbonate.  As  the 
latter  is  a  solid  which  cannot  be  vaporized  (just  like  the  sea  salt) 
it  is  left  in  the  boiler  while  the  water  which  carried  it  evaporates 
and  passes  off  as  steam  to  the  engine  or  other  destination.  Each 
gallon  of  water  fed  in  leaves  its  particles  of  solid  calcium  carbonate 
behind  and  unless  blown  down  and  cleaned  often  enough  the  boiler 
would  become  choked. 

This  calcium  carbonate  by  itself  does  not  form  a  hard  trouble- 
some scale,  but  simply  a  loose  mud-like  coating  which  can  easily 
be  washed  off  the  tubes  and  shell.  In  fact,  a  large  part  of  it 
settles  to  the  bottom  of  the  boiler  or  to  the  mud  drum  of  its  own 
accord,  and  can  easily  be  blown  out.  But,  as  will  be  seen  later, 
when  certain  other  impurities  are  present  in  the  water,  the  cal- 
cium carbonate  is  cemented  into  a  troublesome  scale  along  with 
these  other  impurities. 


FEED-WATER  TREATMENT  159 


MAGNESIUM  CARBONATE 

The  second  commonly  encountered  impurity  in  water  is  mag- 
nesium carbonate.  Its  chemical  formula  is  MgCOa.  It  will  be 
noticed  that  the  only  difference  between  this  formula  and  that  of 
calcium  carbonate  is  that  Mg  in  the  present  case  takes  the  place 
of  Ca  in.  the  previous  one.  Both  are  carbonates,  due  to  their 
carbon  and  oxygen  content. 

Magnesium  is  also  a  metal  and  in  its  pure  state  has  a  bright 
silvery  white  appearance.  Like  calcium  it  never  exists  pure  in 
nature  as  it  has  very  strong  tendencies  to  combine  with  other 
elements.  One  of  its  compounds  which  is  familiar  to  all  is  Epsom 
Salts.  The  chemical  name  for  this  compound  is  magnesium  sul- 
phate, which  is  included  in  our  list  of  commonly  encountered 
impurities  and  about  which  more  will  be  stated  later  on.  Other 
familiar  substances  with  magnesium  in  their  makeup  are  talc, 
asbestos  and  meerschaum.  Magnesia  pipe  covering  is  composed 
principally  of  magnesium  carbonate.  The  combining  .weight  of 
magnesium  is  24.4. 

In  nature,  magnesium  carbonate  exists  quite  extensively  and  is 
known  as  magnesite.  It  also  exists  in  combination  with  calcium 
carbonate,  this  compound  being  known  as  dolomite.  Magnesium 
carbonate  will  not  dissolve  in  pure  water.  But  when  water  con- 
taining COz  comes  in  contact  with  it,  magnesium  bicarbonate — 
MgH2(CO3)2 — is  formed  and  this,  like  the  calcium  bicarbonate,  is 
quite  soluble  in  water.  When  heat  is  applied,  the  bicarbonate 
breaks  up  and  the  CO2  escapes  as  a  gas,  just  as  in  the  case  of  the 
calcium  bicarbonate.  The  passing  off  of  the  CO2  leaves  behind  an 
insoluble  substance  called  magnesium  hydroxide  whose  chemical 
formula  is  Mg(OH)2.  This  precipitate  being  light,  settles  out  of 
the  water  but  slowly,  and  in  the  boiler  where  the  circulation  is 
strong  it  has  a  tendency  to  stay  suspended  and  cause  trouble 
through  priming.  Another  bad  quality  of  this  precipitate  is  its 
cementing  power,  which  is  so  great  that  the  stuff  is  used  for  making 
cement  for  commercial  purposes.  When  it  mixes  with  the  other- 


160  FUEL  ECONOMY  AND  CO2  RECORDERS 

wise  loose  particles   of  precipitated  calcium  carbonate,  a  brittle 
scale  results,  which  cakes  on  the  boiler  surfaces. 


CALCIUM  SULPHATE 

The  chemical  formula  for  calcium  sulphate  is  CaSO4.  All 
the  elements  in  this  compound  are  familiar  to  the  readers  of  these 
lessons  so  it  is  only  the  compound  itself  that  need  be  studied. 
One  of  the  common  substances  composed  of  calcium  sulphate  is 
plaster  of  paris.  Unlike  the  carbonates,  calcium  sulphate  does  not 
require  COz  to  assist  it  to  dissolve.  Pure  water  will  take  just  as 
much  as  water  heavily  charged  with  CO2.  A  fact  that  is  very 
important  to  the  engineer  is  that  calcium  sulphate  is  more  soluble 
in  cool  water  than  in  hot.  According  to  some  authorities  the 
temperature  at  which  the  most  calcium  sulphate  can  be  dissolved 
in  a  given  quantity  of  water  is  about  90  deg.  F.  As  the  tempera- 
ture increases  the  solubility  of  this  compound  gradually  decreases 
until  at  302  deg.  it  is  practically  insoluble.  Because  of  this  char- 
acteristic and  the  fact  that  the  scale  it  forms  is  very  hard  and  has 
great  cementing  powers  over  other  substances,  calcium  sulphate 
is  a  troublesome  and  dangerous  impurity.  Usually  it  can  be 
fought  only  with  suitable  chemical  compounds. 


MAGNESIUM  SULPHATE 

The  fourth  and  last  impurity  we  are  going  to  consider  is  mag- 
nesium sulphate,  although  as  was  stated  that  there  are  several 
others  that  are  sometimes  encountered.  The  chemical  formula  for 
this  compound  is  MgSO4  which,  as  the  name  indicates,  is  the  same 
as  that  for  calcium  sulphate  except  that  magnesium  takes  the  place 
of  the  calcium.  And,  like  the  other  sulphate,  it  dissolves  more 
easily  in  cool  water  than  in  hot.  At  302  deg.  it  precipitates  or 
deposits  as  a  monohydrated  salt,  the  formula  being  MgSO^O. 
It  will  be  noted  that  the  elements  composing  water  (H2O)  have 
been  added.  This  fact  is  indicated  in  the  name  by  the  word 


FEED-WATER  TREATMENT  161 

monohydrated,  mono  meaning  one  and  hydrated  meaning 
watered.  As  used,  the  word  means  that  one  molecule  of  water  has 
been  added  to  or  joined  with  each  molecule  of  magnesium 
sulphate. 

By  itself  magnesium  sulphate  does  not  really  form  a  scale  but 
its  presence  in  feed  water  is  undesirable  because  it  interferes  with 
the  treatment  of  the  impurities  that  do  form  scale. 

METHODS  OF  TREATMENT 

Water  containing  impurities  detrimental  to  good  boiler 
operation  can  be  treated  in  several  ways,  the  method  to  be 
employed  depending  on  the  nature  of  the  impurities  contained. 
For  removing  mud  and  sediment  the  water  may  be  filtered  or  it 
may  be  allowed  to  stand  and  "settle"  before  it  is  fed  into  the 
boiler.  For  what  is  called  temporary  hardness  the  water  may  be 
heated  to  180  deg.  or  more.  Temporary  hardness  is  defined  as 
hardness  which  can  be  eliminated  by  heating  to  or  nearly  to  the 
boiling  point  (212  deg.),  and  is  caused  by  the  carbonates  which,  it 
will  be  remembered,  are  precipitated  by  heat.  Hardness  can  be 
detected  and  its  degree  estimated  by  the  effect  it  has  upon 
soap. 

For  permanent  hardness  more  intense  heat  (to  at  least  302  deg.) 
may  be  applied  as  on  a  closed  heater  or  chemicals  may  be  em- 
ployed. It  is  the  sulphates  that  cause  permanent  hardness 
because  mere  boiling  at  atmospheric  pressure  does  not  eliminate 
them. 

These  two  terms,  temporary  hardness  and  permanent  hardness, 
are  old  names  invented  long  ago  when  chemistry  was  not  as  well 
understood  as  it  is  today.  People  found  that  water  from  certain 
sources  made  soap  curdle  instead  of  producing  a  lather.  Such 
water  they  called  hard.  Next,  they  discovered  that  boiling  some- 
times improved  the  water;  consequently  such  water  was  said  to 
have  temporary  hardness.  Sometimes,  however,  the  water  was 
only  slightly  or  not  at  all  improved  and  such  water  was  said  to 
have  permanent  hardness. 


1 62  FUEL  ECONOMY  AND  CO2  RECORDERS 

Feed  water  may  be  treated  with  chemicals  either  outside  or 
within  the  boiler,  the  former  being  preferable,  because  the  impu- 
rities are  eliminated  before  the  water  is  fed  to  the  boiler  and  so 
blowing  down  and  cleaning  are  required  less  frequently.  When 
treatment  is  administered  before  the  water  is  fed  it  is  advisable  to 
provide  chemicals  for  the  elimination  of  both  the  carbonates  and 
sulphates,  if  both  are  present.  But  when  treatment  is  adminis- 
tered after  the  water  is  fed  only  a  chemical  for  the  sulphates  is 
required,  because  the  heat  takes  care  of  the  carbonates. 


TREATMENT  FOR  CARBONATES 

Calcium  carbonate  can  be  precipitated  before  the  water  is  fed 
to  the  boiler  by  adding  to  it  the  proper  quantity  of  lime,  slaked 
lime  or  caustic  soda. 

The  chemical  formula  for  lime  is  CaO  and  that  for  slaked  lime 
is  CaO2H2,  and  when  either  of  these  is  put  into  water  containing 
calcium  carbonate  (in  the  form  of  calcium  bicarbonate,  due  to  the 
presence  of  CO2)  a  chemical  reaction  takes  place  in  which  the 
calcium  of  the  lime  joins  the  calcium,  carbon  and  oxygen  of  the 
bicarbonate,  producing  two  parts  of  calcium  carbonate  and  the 
hydrogen  of  the  bicarbonate  joins  the  oxygen  and  hydrogen 
of  the  slacked  lime  producing  two  parts  of  water.  The  equa- 
tion is 

CaH2  (CO3)2  +  CaO2H2  =  2  CaCO3  +  2  H2O 

The  calcium  carbonate,  being  insoluble,  drops  out  or  is  pre- 
cipitated. 

The  chemical  formula  for  caustic  soda,  whose  chemical  name  is 
sodium  hydrate,  is  NaOH.  If  this  is  put  into  the  water  instead 
of  the  lime,  part  of  the  carbon  and  oxygen  of  the  calcium  bicar- 
bonate combines  with  it  to  form  sodium  carbonate  (Na2COa) 
which  *is  easily  soluble  in  water.  The  calcium  bicarbonate  being 
robbed  of  part  of  its  carbon  and  oxygen  changes  back  to  calcium 
carbonate  and,  being  insoluble,  it  precipitates  as  before. 


FEED-WATER  TREATMENT  163 

The  treatment  for  magnesium  carbonate  is  exactly  the  same 
as  for  the  calcium  carbonaite. 

TREATMENT  OF  SULPHATES 

Calcium  sulphate  (CaSO4)  can  be  precipitated  by  means  of 
sodium  carbonate,  or  soda  ash  as  it  is  called  commercially.  The 
chemical  formula  for  the  latter  is  Na2CO3.  When  this  compound 


j          Tf 

^^^^r          \9m™« 


FIG.  25. — Apparatus  required  for  proximate  water  analysis. 

is  put  into  water  containing  calcium  sulphate  the  sulphur  and  one- 
quarter  of  the  oxygen  in  the  calcium  sulphate  change  places  with 
the  carbon  in  the  sodium  carbonate,  producing  sodium  sulphate 
and  calcium  carbonate.  The  first  of  these  is  soluble  and  harmless 
and  the  second,  being  insoluble,  precipitates  as  before. 

The  treatment  for  magnesium  sulphate  is  exactly  the  same  as 
for  calcium  sulphate. 

To  secure  desirable  results  in  treating  feed  water  the  quantity 
of  compound  supplied  must  be  proportioned  according  to  the 


1 64  FUEL  ECONOMY  AND  CO2  RECORDERS 

amount  of  scale-forming  impurities  present.  To  estimate  the 
amount  of  impurities  present  necessitates  an  analysis  of  the  water. 
Generally  speaking,  a  water  analysis  can  only  be  made  by  a 
trained  chemist.  It  can  be  attempted  by  others,  but  the  results 
obtained  would  in  most  cases  be  so  inaccurate  as  to  be  useless. 
The  engineer  can,  however,  make  an  approximate  analysis  which 
is  of  some  value  in  indicating  the  character  of  the  water  and  if  the 
analysis  is  made  with  care  and  the  water  does  not  contain  impuri- 
ties that  complicate  its  nature  too  much,  the  kind  and  quantity 
of  scale-preventing  compound  needed  can  be  estimated. 

The  following  method  of  approximate  water  analysis  is  based 
on  that  given  by  John  B.  C.  Kershaw,  in  "Fuel,  Water  and  Gas 
Analysis,"  published  by  D.  Van  Nostrand  Co. 

TEST  APPARATUS 

Assuming  that  the  reader  possesses  the  apparatus  for  making 
the  proximate  fuel  analysis,  as  listed,  the  following  additional 
equipment,  most  of  which  is  shown  in  Fig.  25,  is  required  for  mak- 
ing the  proximate  water  analysis  as  here  outlined: 

Copper  water  bath,  6  in.  diam $i .  50 

Measuring  flask  (200  c.c.  capacity) o .  35 

Porcelain  dish  (22  oz.  capacity) i .  oo 

Glass  stirring  rod o .  10 

Burette,  graduated  in  75  c.c.  (50  c.c.  capacity) 2 .  oo 

Funnel  for  filling  burette o .  10 

Support  or  stand  for  burette  (adjustable) , o .  80 

Measuring  flask  (100  c.c.  capacity) o .  90 

Porcelain  dish  (about  50  c.c.  capacity) 0.15 

i  Glass  funnel  for  filtering  (4-in.) o.  20 

1  Package  of  filter  paper  (8-in.,  i.oo  sheets) 0.35 

$7-45 
The  following  chemical  solutions  are  also  required: 

2  oz.  concentrated  solution  methyl  orange $o. 50 

i  liter — one-fifth  normal  standardized  solution  hydrochloric  acid i .  40 

1  liter — one-fifth  normal  standardized  solution  sodium  carbonate i  .40 

2  oz.  alcoholic   solution   phenol-phthalein o. 50 

$3-80 


FEED-WATER  TREATMENT  165 

If  the  reader  does  not  possess  proximate  fuel-analysis  apparatus 
it  will  also  be  necessary  to  secure  a  bunsen  burner  or  an  alcohol 
or  gasoline  lamp  (such  as  is  shown  in  Fig.  25)  and  an  iron  tripod 
or  adjustable  iron  stand  for  supporting  the  water  bath. 

COPPER  WATER  BATH 

The  copper  water  bath,  shown  on  the  tripod  in  Fig.  25,  is 
employed  when  evaporating  a  sample  of  water  under  conditions 
requiring  a  uniform  heat  at  212  deg.  F.  The  bath  is  fitted  with 
a  lid  composed  of  rings  of  various  diameters  so  that  the  vessel 
containing  the  sample  may  be  conveniently  supported  over  the 
boiling  water.  A  vent  or  spout  at  the  side  and  just  below  the 
top  permits  the  steam  to  escape  without  inconvenience  to  the 
analyst. 

MEASURING  FLASK 

As  the  name  implies,  a  measuring  flask  is  used  to  measure  out 
samples  or  reagents  when  accuracy  is  important.  Its  neck  is 
small  in  diameter,  and  has  a  fine  line  around  it  to  which  level  the 
liquid  to  be  measured  is  poured. 

BURETTE 

The  name  burette  should  be  familiar  to  the  reader,  as  we  em- 
ployed one  in  measuring  flue  gas  when  making  an  analysis  with 
the  Orsat  apparatus.  As  may  have  been  surmised,  "burette" 
means  measuring  vessel.  In  the  present  case  the  burette  is 
employed  to  measure  liquids. 

Acids  neutralize  alkalies  and  vice  versa.  For  instance,  water 
containing  a  quantity  of  some  acid  has  certain  definite  character- 
istics whereby  its  acid  nature  can  be  recognized.  It  will  corrode 
or  eat  away  certain  metals,  say,  iron,  and  it  will,  generally,  change 
a  sensitized  paper  called  litmus  paper  from  blue  to  red.  Now,  if  a 
certain  definite  quantity  of  alkali  is  added  to  this  water  the  latter 
will  lose  its  acid  characteristics — because  the  alkali  has  neutralized 
the  acid  it  contained  by  a  chemical  action  between  them.  If 


1 66  FUEL  ECONOMY  AND  CO2  RECORDERS 

more  alkali  be  added  so  that  the  water  now  contains  a  quantity  in 
excess  of  that  which  was  required  to  neutralize  the  acid,  other 
characteristics  will  be  acquired.  A  definite  quantity  of  alkali  is 
required  to  neutralize  a  given  quantity  of  acid  and  vice  versa. 
For  illustration,  if  a  gallon  of  water  contained,  say,  an  ounce  of  a 
given  acid,  hydrochloric,  for  instance,  it  would  be  found  that  a 
definite  amount  of  some  alkali,  say,  sodium  hydrate,  would  be 
required  to  neutralize  this  acid. 

When  the  amount  of  contained  acid  is  known,  the  amount  of 
the  required  alkali  can  be  calculated.  Hence,  when  the  amount 
of  the  acid  is  unknown,  but  by  experiment  the  required  amount 
of  alkali  is  ascertained,  it  is  possible  to  calculate  therefrom  the 
quantity  of  acid  neutralized. 

This  principle  is  extensively  made  use  of  in  chemistry.  When 
analyzing  water  certain  chemicals  are  added  to  the  sample  being 
analyzed  and  the  amount  of  such  chemicals  required  to  produce  a 
certain  change  is  measured  as  accurately  as  possible.  This  is  the 
purpose  of  the  burette;  it  is  made  long  and  of  small  diameter  so 
that  the  quantity  of  liquid  contained  before  and  after  some  has 
been  let  out  can  be  measured  closely.  When  a  person  adds  chem- 
icals to  a  sample  by  means  of  the  burette  and  measures  the  quan- 
tity required  to  produce  a  certain  change  in  the  character  of  the 
sample,  for  the  purpose  of  estimating  its  original  make-up,  he  is 
said  to  titrate  the  sample.  If  it  is  sodium  hydrate  he  happens  to 
be  adding  he  is  said  to  be  titrating  with  sodium  hydrate. 

When  emptying  the  burette  of  one  compound  and  filling  with 
another,  first  rinse  the  burette  with  distilled  water  and  then  pour 
in  or  rinse  with  a  little  of  the  new  compound  to  be  used  and  drain 
this  out  again  before  the  main  bulk  of  the  new  compound  is  filled 
in. 

INDICATORS 

When  titrating  a  sample  of  water  with  a  certain  chemical  it  is 
often  necessary  or  convenient  to  first  put  some  other  compound 
into  the  water  for  the  purpose  of  indicating  by  change  in  color 
when  the  point  of  neutralization  has  been  reached.  When  a 


FEED-WATER  TREATMENT  167 

compound  is  employed  for  this  purpose  it  is  called  an  indicator. 
Methyl  orange  and  phenoKphthalein  are  used  as  indicators  when 
titrating  with  hydrochloric  acid  or  sodium- carbonate  solutions  to 
ascertain  alkalinity  or  acidity. 

HYDROCHLORIC  ACID  SOLUTION,  ETC. 

The  accuracy  of  results  when  titrating  depends  upon  the  accu- 
racy in  measuring  the  sample,  the  accuracy  in  preparing  the  titrat- 
ing fluid,  the  accuracy  in  reading  the  amount  of  titrating  solution 
required  and  the  accuracy  in  determining  the  point  when  neutrali- 
zation has  been  effected.  As  it  is  important  to  get  the  strength  of 
the  titrating  fluids  as  nearly  correct  as  possible  it  is  recommended 
that  the  one-fifth  normal  standardized  solution  of  hydrochloric 
acid  and  of  sodium  carbonate  be  purchased  ready  made  up.  This 
will  save  bother  and  trouble  and  insure  a  greater  accuracy  than 
can  be  obtained  under  average  conditions  where  proper  facilities 
for  best  work  are  not  present. 

The  bottles  containing  the  solutions  should  always  be  kept  well 
stoppered  so  that  the  strength  will  not  change  due  to  evaporation. 

COLLECTING  SAMPLE 

Care  must  be  exercised  when  collecting  the  sample  to  be  ana- 
lyzed. If  the  water  is  in  an  agitated  condition  a  clean  bottle  or  jar 
can  be  dipped  into  the  tank  or  reservoir  at  almost  any  point  and 
filled  in  the  ordinary  way.  If  it  is  more  convenient  to  tap  the 
supply  main,  a  good  arrangement  is  to  allow  a  small  stream  of 
water  to  run  into  a  clean  barrel  or  tub  continuously  and  dip  the 
sample  therefrom.  The  main  thing  is  to  be  sure  that  the  bottle  to 
contain  the  sample  and  the  barrel  or  tub,  if  any  is  employed,  are 
clean,  and  will  not  pollute  the  water  with  foreign  matter  which  it 
does  not  contain  naturally.  A  sample  of  from  2  qt.  to  i  gal.  is 
sufficient. 

TEST  FOR  ALKALINITY 

The  first  step  of  the  analysis  is  to  test  whether  the  water  is 
alkaline  or  acidulous  in  nature.  Usually  it  is  alkaline,  but  some- 


1 68       FUEL  ECONOMY  AND  CO2  RECORDERS 

times,  when  the  water  comes  from  boggy  land,  it  may  be  slightly 
acid  in  character. 

To  test  for  alkalinity  fill  the  2oo-c.c.  measuring  flask,  first  seeing 
that  it  is  thoroughly  clean,  with  the  test  water,  so  that  the  level 
is  exactly  at  the  line  which  will  be  found  around  the  neck  of  the 
flask.  Empty  this  water  into  the  clean  22-02.  basin  and  rinse  the 
flask  with  distilled  water,  putting  the  rinsings  into  the  basin  also. 

Distilled  water  may  be  purchased  by  the  bottle,  or  if  much  is  to 
be  used,  a  home-made  or  purchased  still  may  be  found  more 
economical. 

Add  to  the  200  c.c.  of  test  water  in  the  basin  two  drops  of  the 
concentrated  solution  of  methyl  orange.  Next,  put  into  the  bur- 
ette some  of  the  one-fifth  normal  standardized  solution  of  hydro- 
chloric acid  and  read  the  level  at  which  the  acid  stands  with  great 
care  and  as  accurately  as  possible.  Now,  titrate  by  opening  the 
cock  of  the  burette  a  small  amount,  allowing  some  of  the  acid  to 
fall  into  the  basin  of  test  water  drop  by  drop,  stirring  the  water  all 
the  while  with  the  glass  rod,  until  the  color  of  the  water  changes 
from  canary  yellow  to  orange  and  finally  to  faint  pink.  Shut 
off  the  acid  at  this  point  and  again  read  the  level  in  the  burette  as 
closely  as  possible.  When  reading  the  burette  take  as  the  level 
of  the  liquid  the  bottom  of  the  slight  curve  which  the  surface  of  the 
liquid  assumes  due  to  the  narrowness  of  the  tube. 

The  analysis  of  a  water  sample  is  usually  expressed  in  parts  by 
weight  of  impurities  per  100,000  parts  of  water.  Thus,  when  a 
water  is  said  to  contain  20  parts  of  calcium  carbonate  what  is 
really  meant  is  that  every  100,000  Ib.  of  water  contain  20  Ib.  of 
this  compound. 

TEMPORARY  HARDNESS 

The  test  with  hydrochloric  acid  as  described  above  indicates  the 
temporary  hardness  of  the  water  and  this  is  assumed  to  be  caused 
by  the  presence  of  calcium  carbonate  in  the  water.  To  estimate 
the  parts  of  calcium  carbonate  per  100,000  multiply  the  number  of 
cubic  centimeters  of  acid  required  by  5. 

To  illustrate,  if  it  took  4.1  c.c.  of  the  one-fifth  normal  standard- 


FEED-WATER  TREATMENT  169 

ized  acid  solution  to  neutralize  a  2oo-c.c.  sample  of  water  the 
parts  of  calcium  carbonate  per  100,000  parts  of  water  would  be 
taken  as 

4.1  X  5  =  20.5 

TEST  FOR  ACIDITY 

If  the  water  to  be  examined  is  acidulous  the  following  method 
must  be  employed: 

Carefully  measure  out  as  before  200  c.c.  of  the  water  to  be  tested 
and  add  two  drops  of  the  phenol-phthalein  instead  of  the  methyl 
orange.  Load  the  burette  with  the  one-fifth  normal  standardized 
solution  of  sodium  carbonate  and  titrate  as  before,  reading  off  as 
accurately  as  possible  the  number  of  cubic  centimeters  required  to 
change  the  color  of  the  water  to  a  purple-red  tint.  The  number 
of  cubic  centimeters  thus  required  is  then  multiplied  by  the  factor 
5  to  give  the  alkali  equivalent  of  the  acid  present  in  the  water. 
Thus,  if  1.3  c.c.  of  the  sodium  carbonate  was  used  in  titrating  the 
water  contained  acid  equivalent  to  a  sodium  carbonate  content  of 

i-3  X  5  =  6.5  parts 
per  100,000. 

PERMANENT  HARDNESS 

The  permanent  hardness  or  hardness  due  to  the  sulphates  is 
ascertained  by  the  following  test: 

Filter  a  little  more  than  100  c.c.  of  the  water  to  be  tested  and 
then  measure  exactly  100  c.c.  into  a  clean  vessel  and  add  from  the 
burette  exactly  25  c.c.  of  the  standardized  sodium-carbonate 
solution.  Evaporate  this  mixture  to  dryness  in  a  porcelain  dish 
on  the  water  bath.  Next,  pour  into  the  dish  about  100  c.c.  of 
distilled  water,  heat  gently  and  stir  to  insure  complete  solution  of 
the  soluble  solid  matter  in  the  dish.  Next,  filter  the  solution  care- 
fully and  wash  the  filter  well  by  pouring  warm  distilled  water  into 
it  after  the  solution  has  passed  through.  Collect  the  filtered  so- 
lution and  the  filter  washings  in  the  large  porcelain  basin,  add  two 


170  FUEL  ECONOMY  AND  CO2  RECORDERS 

drops  of  methyl  orange,  titrate  with  the  one-fifth  normal  standard- 
ized hydrochloric  acid  and  read  carefully  the  number  of  cubic 
centimeters  required  to  cause  the  change  from  canary  yellow  to 
faint  pink.  The  number  of  cubic  centimeters  of  the  acid  solution 
required  to  bring  about  the  color  change  is  subtracted  from  25  and 
the  result  multiplied  by  5  to  give  the  degrees  of  permanent  hard- 
ness, expressed  in  their  equivalent  of  parts  of  calcium  carbonate 
per  100,000  parts  of  water. 

ESTIMATING  TREATMENT 

It  is  stated  by  reliable  authorities  that  water  which  contains 
more  than  20  parts  per  100,000  of  impurities,  causing  permanent 
and  temporary  hardness,  should  be  treated  before  use.  Whether 
the  treatment  should  be  made  before  the  water  is  fed  to  the  boiler 
is  largely  a  matter  of  size  of  plant  or  amount  of  water  used. 

The  quantity  of  lime  required  to  treat  water  for  temporary 
hardness  (calcium  and  magnesium  carbonates)  may  be  estimated 
as  follows:  Pounds  of  fresh  baked  lime  required  per  1000  gal.  of 
water  equals  number  of  parts  of  calcium  carbonate  in  100,000  (as 
shown  by  test  for  temporary  hardness)  multiplied  by  0.0467. 

The  pounds  of  slaked  lime  required  per  1000  gal.  of  water  equals 
the  number  of  parts  of  calcium  carbonate  multiplied  by  0.0617. 

And  the  pounds  of  caustic  soda  (sodium  hydrate)  required  per 
1000  gal.  of  water  equals  the  number  of  parts  of  calcium  carbonate 
multiplied  by  0.0667. 

TREATMENT  FOR  SULPHATES 

When  lime  is  used  for  treating  the  carbonates  the  quantity  of 
sodium  carbonate  or  soda  ash  required  to  correct  the  permanent 
hardness  may  be  estimated  as  follows:  Pounds  of  soda  ash 
required  per  looogal.  of  water  equals  number  of  parts  solid  matter 
causing  permanent  hardness,  multiplied  by  0.0884. 

When  caustic  soda  is  used  for  the  carbonates  not  so  much  soda 
ash  is  required  for  the  sulphates  for  the  reason  that  the  caustic 
soda  and  the  carbonates  react  chemically  to  produce  sodium  car- 


FEED-WATER  TREATMENT  171 

bonate  (soda  ash)  which  becomes  available  to  react  with  the  sul- 
phates to  produce  sodiunr  sulphate  and  calcium  and  magnesium 
carbonates  (the  latter  being  insoluble). 

To  estimate  the  quantity  of  soda  ash  required  for  the  sulphates 
in  such  a  case,  proceed  as  usual  to  estimate  the  quantity  required 
as  though  lime  were  to  be  used  for  the  carbonates.  Then, 
subtract  from  the  quantity  thus  found,  *££•  times  the  quantity  of 
caustic  soda  used  for  the  carbonates. 

The  foregoing  materials  for  treating  water  are  never  100  per 
cent,  pure  when  bought  in  bulk  and,  consequently,  it  is  necessary 
to  allow  for  this  when  making  up  a  treatment.  The  first  step  is  to 
find  out  from  the  dealer  what  the  percentage  of  purity  is,  then 
divide  this  percentage  into  the  quantity  actually  required  as 
estimated  above  and  multiply  the  result  by  100. 

TESTING  TREATED  WATER 

It  is  well  to  test  the  treated  water  occasionally  to  make  sure 
that  the  treatment  is  correctly  proportioned.  For  thispurpose  the 
following  additional  material  is  needed:  About  a  liter  of  standard- 
ized alcoholic  soap  solution  of  such  strength  that  when  employing  a 
200-c.c.  sample  of  water,  i  c.c.  of  the  solution  will  be  equivalent  to 
five  parts  of  calcium  carbonate  per  100,000  parts  of  water,  also 
about  2  oz.  of  a  weak  solution  of  silver  nitrate. 

The  test  is  conducted  as  follows: 

Partly  fill  an  ordinary  drinking  glass  with  some  of  the  treated 
water  which  it  is  desired  to  test.  Into  this  put  a  few  drops  of  the 
silver  nitrate  solution  and  note  whether  a  snowy  precipitate  is 
formed  or  a  brownish  color  is  given  to  the  water.  The  snowy  pre- 
cipitate is  caused  by  the  presence  of  carbonates  and  indicates  that 
the  quantity  of  lime  should  be  increased.  The  brown  color  indi- 
cates an  excess  of  lime. 

Next  draw  a  fresh  sample  of  exactly  200  c.c.  and  pour  it  into  a 
clean  bottle  of^such  size  that  the  sample  will  not  more  than  half 
fill  it.  Put  some  of  the  soap  solution  into  the  burette  and  read  the 
quantity  as  accurately  as  possible.  Next,  run  a  small  quantity  of 
the  solution  into  the  bottle  containing  the  test  sample,  shake  the 


172  FUEL  ECONOMY  AND  CO2  RECORDERS 

bottle  vigorously  for  a  minute  or  two  and  note  whether  a  lather  is 
formed.  Continue  to  add  soap  solution  and  shake  until  a  lather 
is  formed  which  will  cover  the  whole  surface  of  the  water  when  the 
bottle  is  lying  on  its  side  and  remain  for  five  minutes.  When  this 
point  is  reached,  read  on  the  burette  scale  the  number  of  cubic  cen- 
timeters of  soap  solution  that  was  used.  This  number  multiplied 
by  5  roughly  indicates  the  total  hardness  in  equivalent  parts  of 
calcium  carbonate  per  100,000  parts  of  water. 

Finally,  measure  out  another  fresh  sample,  exactly  200  c.c.  in 
quantity,  and  put  this  into  the  22-02.  porcelain  dish.  Then,  add 
to  the  sample  two  drops  of  methyl  orange  and  two  or  three  drops 
of  the  phenolphthalein.  Titrate  with  the  standardized  hydro- 
chloric-acid solution  and  note  the  number  of  cubic  centimeters  of 
the  solution  required  to  change  the  red  color  of  the  sample  to  a 
yellow  shade.  Then,  run  in  more  of  the  acid  solution  and  read  off 
the  quantity  required  to  turn  the  yellow  to  pink.  The  first 
reading  multiplied  by  10  gives  the  causticity,  while  the  total 
cubic  centimeters  of  the  acid  solution  used,  multiplied  by  5,  gives 
the  alkalinity. 

If  the  total  hardness,  as  shown  by  the  soap  test,  is  greater  than 
the  alkalinity,  it  indicates  insufficient  proportion  of  soda  ash  in 
the  treatment  If  the  total  hardness  is  less  than  the  alkalinity  it 
indicates  a  too  great  proportion  of  soda  ash.  If  the  alkalinity  is 
greater  than  the  causticity  it  indicates  an  insufficient  proportion  of 
lime.  If  the  causticity  is  greater  than  the  alkalinity  it  indicates 
an  excess  of  lime. 

The  method  of  estimating  from  the  results  obtained  from  the 
foregoing  tests,  what  changes  to  make  in  the  quantities  of  lime  and 
soda  ash,  is  exactly  the  same  as  that  employed  in  making  up  the 
original  quantities.  To  illustrate,  if  the  alkalinity  is  greater  than 
causticity  by  1.5  c.c.  of  acid  or 

1.5  X  5  =  7.5  parts  per  100,000 

the  weight  of  the  lime  supplied  per  1000  gal.  of  water  should  be 
increased  by 

7.5  X  0.0467  =  0.35  Ib. 


FEED-WATER  TREATMENT  173 

If  it  should  happen  that  the  causticity  was  greater  than  the 
alkalinity  by  1.5  c.c.,  or  7. 5- parts  per  100,000,  then  the  weight  of 
the  lime  supplied  should  be  decreased  by  0.35  Ib.  per  1000  gal.  of 
water  treated. 

OTHER  SCALE  REMEDIES 

In  addition  to  the  staple  chemicals  dealt  with  here  many  other 
chemicals  or  preparations  have  been  suggested  and  tried  as  scale 
preventives.  Even  such  ordinary  products  as  potatoes,  tanbark, 
molasses,  etc.,  have  had  their  supporters.  In  addition,  are  the 
many  proprietary  preparations  which  have  been  placed  on  the 
market. 

Kent's  "Mechanical  Engineers'  Pocketbook"  states: 

"In  cases  where  water  containing  large  amounts  of  total  solid 
residue  is  necessarily  used,  a  heavy  petroleum  oil,  free  from  tar  or 
wax,  which  is  not  acted  upon  by  acids  or  alkalies,  not  having 
sufficient  wax  in  it  to  cause  saponification,  and  which  has  a 
vaporizing  point  at  nearly  600  deg.  F.,  will  give  the  best  results 
in  preventing  boiler  scale.  Its  action  is  to  form  a  thin,  greasy 
film  over  the  boiler  linings,  protecting  them  largely  from  the 
action  of  acids  in  the  water  and  greasing  the  sediment  which 
is  formed,  thus  preventing  the  formation  of  scale  and  keeping 
the  solid  residue  from  the  evaporation  of  the  water  in  such 
a  plastic  suspended  condition  that  it  can  be  easily",  ejected  from 
the  boiler  by  the  process  of  'blowing  off.'  If  the  water  is  not 
blown  off  sufficiently  often  this  sediment  forms  into  a  'putty' 
that  will  necessitate  cleaning  the  boilers.  Any  boiler  using  bad 
water  should  be  blown  off  every  12  hr." 

At  one  time  kerosene  oil  was  used  somewhat  extensively,  its 
action  being  similar  to  that  of  the  heavy  petroleum  oil  mentioned 
in  the  foregoing  paragraph.  B ut  the  frequency  of  accidents  due  to 
carrying  an  open  flame  into  boilers  in  which  kerosene  had  been 
used  caused  its  use  to  be  largely  abandoned. 

Recently,  graphite  has  been  brought  into  prominence  as  a  scale 
preventive  and  many  engineers  will  testify  that  it  has  produced 
beneficial  results.  Its  action  is  mechanical  rather  than  chemical. 


174       FUEL  ECONOMY  AND  CO2  RECORDERS 

Fed  into  the  boiler  with  the  water  at  regular  intervals  and  in 
stated  quantities,  it  tends  to  form  a  coating  on  the  heating  sur- 
face of  the  boiler  which  prevents  the  scale  from  adhering.  The 
graphite  also  intermixes  with  the  crystals  of  the  scale-forming 
impurities  and  prevents  them  from  cementing  solidly  together  so 
that  they  exist  only  as  a  sludge  or  form  of  mud  which  can  easily 
be  blown  out. 

The  chapter  on  feed- water  treatment  has  of  necessity  dealt  with 
only  the  most  common  of  the  troublesome  impurities  encountered 
in  water.  Water  from  some  sections  contains  many  other  impu- 
rities which  have  not  been  discussed  here  because  of  the  difficulty  of 
the  analysis  necessary  to  detect  them.  Some  of  these  cause  pitting 
and  corrosion  and  are  really  dangerous  when  neglected.  In 
some  cases  the  nature  of  the  water  may  be  such  that  unless  the 
treatment  is  very  carefully  planned  and  executed  the  effects  pro- 
duced may  be  as  bad  as,  or  worse  than,  the  effects  of  the  original 
water. 

Taken  as  a  whole  the  subject  of  water  analysis  and  treatment  is 
really  so  complex  as  to  require  the  study  of  trained  chemical 
experts.  Trying  to  diagnose  and  cure  feed-water  troubles  by 
home  methods  and  remedies  is  much  like  trying  to  diagnose  and 
cure  human  ills  by  home  treatment.  It  works  well  enough  when 
the  trouble  is  simple  and  slight  but  in  the  long  run  it  is  often  safest 
and  cheapest  to  consult  a  good  specialist  who  knows  what  to  look 
for  and  how  to  prescribe  and  apply  the  remedy. 


CHAPTER  XI 

CO 2  RECORDERS 
HOW  A  CO  2  RECORDER  WORKS 

When  you  use  a  sponge  to  soak  up  water  from  the  floor  you  do 
not  consider  that  anything  remarkable  has  happened.  You  have 
seen  the  tanks  at  the  gas  works  rise  as  they  filled  with  gas,  and  drop 
down  as  the  gas  was  discharged,  and  you  thought  that  a  usual 
proceeding. 

The  principal  reasons  why  a  CO2  recorder  records  CO2  are  really 
no  more  mysterious  nor  remarkable  than  the  absorption  of  water 
by  a  sponge,  or  the  inflation  of  a  tank  by  gas.  Practically,  the 
same  physical  actions  occur  in  both  cases,  but  the  things  we  use 
are  different. 

Because  chemicals  have  unfamiliar  names  is  no  reason  why  we 
should  shy  at  them  any  more  than  we  shy  at  a  yeast  cake,  which  is 
a  chemical.  Some  chemical  solutions  absorb  certain  gases  just 
as  a  sponge  absorbs  water.  You  know  that  to  relieve  a  gas-bound 
ammonia  pump  you  let  the  gas  discharge  into  a  pail  of  water.  If 
the  gas  were  discharged  into  the  room  the  fumes  would  be  quite 
disagreeable,  but  when  discharged  into  the  water  the  gas  is 
absorbed  like  water  by  a  sponge. 

Platinum  sponge  will  absorb  a  surprisingly  large  amount  of 
hydrogen  gas,  and  the  sponge  will  not  increase  in  volume.  To 
prove  that  it  will  absorb  this  gas  we  will  arrange  two  bottles,  as  in 
Fig.  26.  One  is  filled  with  water,  the  other  with  hydrogen  gas. 
We  suspend  a  piece  of  platinum  sponge  in  the  gas  as  shown.  The 
sponge  will  then  absorb  the  gas,  create  a  vacuum  in  the  bottle  and 
draw  into  it  water  from  the  other  bottle. 

The  first  experiment  showed  that  some  substances  do  absorb 


i76 


FUEL  ECONOMY  AND  CO2  RECORDERS 


gas.  We  will  now  experiment  with  a  sample  of  flue  gas  of  100  c.c. ; 
12  per  cent,  is  CO2  and  the  other  88  per  cent,  is  made  up  of 
other  gases. 

We  have  four  bottles,  Fig.  27,  one  containing  100  c.c.  (cubic 
centimeters)  of  water;  one,  100  c.c.  of  flue  gas;  one  with  a  caus- 
tic-potash solution  and  the  last  bottle  we  will  consider  inverted 
and  full  of  water.  Opening  the  pinch  cocks  on  the  rubber  tubes 
connecting  the  bottles,  lift  the  water  bottle  to  the  position  indi- 
cated by  the  dotted  lines.  The  water  flows  into  the  second  bottle, 


FIG.  26. — Platinum  sponge  absorbing  gas. 

forcing  the  100  c.c.  of  flue  gas  out,  causing  it  to  bubble  up  through 
the  caustic-potash  solution.  After  the  gas  has  passed  through  the 
solution,  an  analysis  would  show  no  €62,  but  it  would  show  that 
88  c.c.  of  other  gases  were  present.  At  the  beginning  of  the  experi- 
ment the  inverted  bottle  is  filled  with  water  and  is  sealed  by  a 
little  water  in  the  jar,  just  as  the  spring- water-bottle  drinking 
fountains  are  arranged.  If  the  flue  gas  contains  12  per  cent. 
CC>2  and  this  bottle  is  lifted  as  the  gas  comes  into  it,  so  that  the 
water  levels  in  the  jar  and  bottle  are  the  same,  the  water  will 
run  down  to  the  88  c.c.  or  per  cent,  mark  and  the  gas  will  be  at 
atmospheric  pressure,  as  it  has  been  throughout  the  experiment. 


CO2  RECORDERS 


177 


FIG.  2 /.—Experiment  to  Show  that  Caustic-Potash  Absorbs  CO2. 


i78 


FUEL  ECONOMY  AND  CO2  RECORDERS 


The  other  12  per  cent,  of  the  gas  or  the  CC>2  did  not  get  through  the 
caustic  potash.  This  experiment  demonstrates  that  a  caustic- 
potash  solution  absorbs  only  the  CC^in  the  flue  gases  but  allows 


CHA.RT 
DRUM 


FIG.  28.— The  Essentials  of  a  CO2  Recorder. 

the  other  gases  to  pass  through.    About  the  same  process  as  that 
gone  through  in  this  last  experiment  goes  on  in  a  CO2  recorder. 

In  the  recorder  the  chemical  or  "  sponge"  which  absorbs  the  CO2 
is  caustic  potash.    The  pen  which  marks  the  chart  is  attached  to 


CO,  RECORDERS  179 

the  top  of  a  gas  bell  that  rises  and  falls  as  it  is  filled  with  and  emp- 
tied of  the  CO2  gas,  just  as  the  tanks  at  the  gas  works  rise  and  fall. 

Before  continuing,  let  us  understand  why  we  say  such  and  such 
a  percentage  of  CO2-  Percentage  means  "by  the  hundred,"  and 
10  per  cent  or  12  per  cent,  means  10  or  12  parts  of  a  total  of  100 
parts.  The  total  of  100  parts,  or  100  per  cent.,  may  be  any  quan- 
tity we  choose  to  make  it.  In  measuring  CC>2,  all  or  100  per  cent, 
of  the  sample  of  gas  taken  from  the  flue  is  100  cubic  centimeters 
(c.c.),  or  a  little  over  6  cu.  in.  When  the  flue-gas  analysis  shows 
12  per  cent  CO2  we  know  that  12  parts,  or  12  c.c.,  of  the  100 
parts,  or  100  c.c.,  is  CO2  gas. 

Fig.  28  shows  the  essentials  of  a  CO2  recorder,  and  when  you 
understand  it,  you  will  understand  how  and  why  any  CC>2  recorder 
works.  The  gas  is  brought  from  the  boiler  uptake  and  passed  up 
through  the  filter,  which  contains  a  bottle  nearly  filled  with  oil  or 
water  to  take  out  the  soot  in  the  sample.  Gas  flows  into  the 
measuring  bottle,  which  holds  exactly  100  c.c.  The  sample  hav- 
ing been  measured,  it  goes  to  the  "  sponge,"  or  caustic-potash  so- 
lution, where  all  the  CO2  gas  is  absorbed,  and  the  rest  bubbles 
through  the  solution  and  fills  the  receiver  bottle.  From  the 
receiver  bottle  the  gas  is  led  to  the  gas  bell,  which  has  a  water  seal 
so  that  gas  cannot  escape  to  the  atmosphere.  This  bell  and  the 
pen  arm  rise  and  mark  the  chart  against  which  the  pen  bears. 
When  the  mark  is  made  the  gas  goes  back  through  the  pipe  and 
eventually  goes  to  the  atmosphere.  The  chart  drum  is  revolved 
by  clockwork,  as  usual. 

As  the  caustic  potash  absorbs  only  CO2  we  see  that  if  the  meas- 
ured sample  is  high  in  CC>2,  there  will  be  less  gas  going  through  the 
solution  to  fill  the  gas  bell,  and  the  pen  will  not  make  as  long  a 
mark  as  when  more  gas  is  passing  through  the  solution.  On  a 
recording  steam  gage  or  thermometer  the  pen  makes  a  longer 
mark  as  the  pressure  or  temperature  increases  from  the  zero  point 
on  the  chart  This  is  not  so  with  the  CO2  recorder  of  this  sort. 
The  greater  the  CO2  percentage,  the  shorter  the  mark. 

To  get  the  gas  into  and  out  of  the  measuring  and  receiving  bot- 
tles, caustic-potash  tanks,  gas  bell,  etc.,  many  siphons  and  traps 


i8o  FUEL  ECONOMY  AND  CO2  RECORDERS 

are  required.  The  motive  power  for  most  CO2  recorders  is  a 
stream  of  water  flowing  from  a  pet-cock.  As  the  stream  is 
increased  the  machine  works  faster;  that  is,  it  makes  a  greater 
number  of  readings  per  hour.  With  the  usual  CO2  machine 
about  seven  or  eight  readings  per  hour  will  produce  a  good 
chart. 

CO2  RECORDER  TROUBLES 

The  most  common  of  CO2  recorder  troubles  is  that  due  to  air 
leaks  in  the  pipe  line  carrying  the  flue  gas  to  the  recorder.  This 
line  is  under  a  slight  vacuum  and,  unless  extreme  care  is  used  in 
"making  up"  the  joints  air  will  get  into  the  pipe  and  dilute  the 
gas,  giving  a  lower  CO2  reading  than  is  correct.  In  cutting  the 
pipe  for  these  lines  make  the  threads  large  and  use  new  fittings  to 
insure  tight  joints.  Do  not  attempt  to  spring  the  pipe  very 
much  to  make  up  a  union  as  leaks  are  likely  to  develop.  Some 
soot  will  lodge  in  the  gas  line  and  because  of  this  no  ragged  edges 
should  be  left  on  the  inside  of  the  pipe  for  these  edges  tend  to 
hold  the  soot  and  cause  it  to  accumulate  at  these  points,  reducing 
the  area  of  the  pipe.  It  is  a  good  plan  to  provide  the  pipe  so  that 
a  compressed-air  hose  connection  may  be  made  for  blowing  soot 
from  the  pipe. 

The  water  which  furnishes  the  motive  power  for  the  recorder 
is  often  raised  to  the  supply  tank  by  a  motor  driven  centrifugal 
pump.  This  outfit  should  get  adequate  attention  as  regards 
cleaning  and  protection  from  dust  and  water.  Because  it  gives 
little  trouble  it  is  likely  to  be  neglected. 

When  the  water  and  solution  as  well  as  the  oil  in  the  filters  are 
changed,  clean  the  containers  thoroughly,  for  dirt  will  give  as 
much  trouble  as  anything  else  about  a  CO2  recorder. 

No  definite  rule  as  to  interval  between  renewals  of  the  solution 
can  be  given  to  apply  to  all  machines,  but  where  machines  are 
used  steadily  day  and  night  and  each  solution  tank  holds  about 
three  quarts,  the  solution  should  be  renewed  at  least  every  three 
weeks.  At  the  end  of  this  time  the  solution  will  have  absorbed  so 


CO2  RECORDERS  181 

much  CO2  gas  that  its  ability  to  absorb  all  of  that  contained  in 
the  gas  samples  admitted  to  the  tank  will  be  greatly  impaired 
and,  of  course,  correct  readings  will  not  be  made. 

PROPER  STRENGTH  OF  SOLUTION 

It  is  necessary  that  the  caustic  potash  solution  for  absorbing 
the  CC>2  be  of  sufficient  strength.  A  good  solution  may  be  had 
by  dissolving  one-half  pound  of  commercial  caustic  potash  to  a 
quart  of  water. 

The  average  fireman  is  claimed  to  be  a  dense  individual. 
"You  can't  learn  him  anything"  is  what  is  usually  said  of  him. 
However  "thick"  he  may  be,  it  doesn't  take  him  long  to  learn 
how  to  beat  a  CC>2  recorder  or  an  average  gas  sample  collector, 
especially  if  he  is  paid  a  bonus  based  on  the  CC>2  percentage  he 
is  able  to  show  on  the  chart. 

Where  sample  collectors  are  used  and  where  the  firemen  are 
practically  told  that  they  must  produce  so  and  so  much  CO2  or 
find  another  job,  they  regard  the  job  as  important  enough  to  show 
good  CO2  results  however  correctly  or  honestly  the  results  are 
obtained. 

A  favorite  trick  where  sampling  cans  are  used,  is  to  fire  any  old 
way  until  near  the  time  to  be  relieved.  About  this  time  the  boiler 
or  boilers  served  by  the  can  are  coaled  and  conditions  made  so 
that  a  gas  high  in  €62  is  produced.  The  can  is  then  quickly  filled 
with  water  and  then  quickly  emptied,  thus  drawing  into  it  an 
instantaneous  sample  of  the  gas  containing  a  high  percentage  of 
CO2.  Analysis  shows  a  high  CO2  and  the  fireman  is  credited 
with  an  excellent  day's  work  and  some  extra  pay  besides.  He 
invariably  "kills"  the  good  thing,  however, by  getting  results  that 
excite  suspicion,  or  by  dropping  the  pressure  due  to  "loafing"  of 
the  boilers  while  he  is  getting  ready  to  draw  the  sample.  By 
enclosing  the  valves  and  cocks  connecting  the  tank  with  the  water 
inlet  and  outlet,  in  a  locked  box,  this  form  of  deception  may  be 
avoided. 

It  must  be  admitted  that  it  is  better,  from  an  engineering 
standpoint  to  have  a  multiple  recorder  when  COz  charts  are  to  be 


1 82       FUEL  ECONOMY  AND  CO8  RECORDERS 

taken  from  more  than  one  boiler  at  one  time.  With  such  a 
machine  the  chances  for  successful  deception  by  the  firemen  are 
made  remote.  The  objection  to  the  multiple  machine  or  a  sepa- 
rate machine  for  each  boiler  is  the  high  investment  cost,  as  com- 
pared to  a  single  machine  piped  to  all  the  boilers  with  cocks  to 
connect  the  recorder  to  any  desired  boiler. 

When  a  single  machine  is  so  connected,  the  "header"  to  which 
the  lines  from  all  boilers  connect  with  the  single  pipe  leading  to 
the  machine,  should  be  boxed  and  locked,  so  that  the  firemen 
cannot  tell  by  the  position  of  the  cocks  which  boiler  the  recorder 
is  serving.  Even  when  the  cocks  are  so  encased  a  fireman  can 
so  tell  to  what  boiler  the  machine  is  connected.  He  "juggles" 
each  fire  separately,  covering  it  carefully  and  rather  heavily, 
closing  the  back  damper  a  trifle.  Then  he  observes  the  readings. 
The  boiler  to  which  special  attention  has  been  given  will  show 
the  results  on  the  chart.  When  he  finds  the  proper  boiler,  that 
one  gets  the  most  of  his  careful  attention  for  the  rest  of  the  day. 

As  nearly  every  fireman  likes  to  be  credited  with  a  good  day's 
work  even  though  he  does  not  get  a  bonus  he  will  take  advantage 
of  these  opportunities  to  make  a  good  showing.  For  this  reason 
it  is  best,  where  financial  conditions  permit,  to  install  a  multiple 
machine  or  a  single  machine  for  each  boiler. 

CARING  FOR  THE  RECORDER 

Any  CO2  recorder  is  a  delicate  apparatus  and  needs  the  atten- 
tion of  someone  competent  to  care  for  it  without  doing  more 
damage  than  good.  This  is  a  point  commonly  neglected,  as  one 
finds  many  plants  in  which  the  firemen,  oilers,  engineers  and, 
sometimes  the  cleaners  and  polishers  all  jointly  take  a  hand  in 
"gettin'  'er  goin'."  It  is  the  engineer's  duty  to  look  after  the 
recorder  and  he  should  do  so  and  also  instruct  an  assistant  or  one 
fireman  in  handling  it  and  then  hold  him  responsible  for  it,  giving 
everybody  else  to  understand  that  they  are  to  keep  their  hands 
off  it. 

While  the  CC>2  recorder  is  a  necessity  in  any  large  up-to-date 
boiler  room/  like  all  other  recording  instruments,  the  record 


C02  RECORDERS  183 

from  it  must  be  studied  and  compared  and  action  taken  on  what 
they  show  to  be  of  maximum  value.  These  machines  cost  con- 
siderable and  represent  a  large  investment.  To  simply  file  the 
charts  without  studying  them  would  be  like  putting  money  in  a 
bank  that  paid  i  per  cent,  interest  instead  of  taking  advantage  of 
opportunities  to  get  6  per  cent. 

CORRECT  LOCATION  FOR  SAMPLE  PIPE 

It  is  just  as  important  to  locate  the  gas  line  in  the  gas  path  to 
insure  getting  correct  samples  as  it  is  to  have  the  line  air  tight. 
It  is  quite  common  to  find  gas  sample  pipes  so  placed  in  the  boiler 
that  the  samples  being  drawn  are  not  truly  representative  of  the 
quality  of  the  gas  passing  out  of  the  boiler.  The  proper  location 
for  the  sample  pipe  in  any  boiler  will  be  in  the  center  of  the  gas 
path  and  on  the  boiler  side  of  the  damper  at  the  point  where  the 
gases  leave  the  boiler.  This  does  not  mean  to  place  the  pipe  in 
the  center  of  the  opening  through  which  the  gases  travel  as  they 
leave  the  boiler,  but  in  the  center  of  the  gas  stream  itself.  For 
example,  in  a  boiler  of  the  B.  &  W.  type  the  center  of  the  gas 
stream  is  usually  below  the  center  of  the  outlet  opening. 

To  be  sure  to  locate  the  center  of  the  gas  stream  take  several 
samples  from  several  different  places  in  the  stream.  The  place 
at  which  the  composition  of  the  gas  varies  most  widely  may  be 
considered  as  the  place  to  permanently  locate  the  pipe,  for  above 
and  below  and  at  the  extreme  sides  of  the  stream  the  gas  velocity 
is  usually  less  than  in  the  center  and  "eddies"  form. 

AIR  LEAKS 

When  it  is  known  that  the  baffling,  doors  and  brickwork  of  all 
the  boilers  are  tight  and  when  different  firemen  stoke  the  same 
boiler  at  different  times  and  still  the  COz  produced  in  this  par- 
ticular boiler  is  lower  than  in  others  in  the  plant,  it  indicates  that 
the  gas  line  is  improperly  located  or  leaks  air.  It  is  important 
also  to  make  sure  that  air  does  not  leak  in  at  the  point  where  the 
pipe  enters  the  settings,  although  the  pipe  inside  the  setting  should 


184       FUEL  ECONOMY  AND  CO2  RECORDERS 

be  long  enough  so  that  a  leak  here  would  not  seriously  effect  the 
reading. 

When  rubber  tubes  are  used  to  connect  the  gas  pipe  to  the 
recorder  or  when  used  to  connect  different  parts  of  the  machine 
they  must  be  watched  for  leaks.  The  recorder  is  usually  located 
where  the  room  temperature  is  high  and  eventually  the  rubber 
will  harden  and  crack.  Enough  tubing  should  be  carried  in  stock 
to  replace  old  tubing  and  avoid  taking  the  recorder  out  of  service. 
Where  parts  of  the  recorder  are  connected  together  by  small 
union  fittings  it  should  be  known  that  these  are  tight,  when 
it  is  found  difficult  to  get  such  fittings  tight,  they  may  be  screwed 
up  and  soap  used  to  seal  the  joints  until  they  can  be  renewed  or 
repaired. 

FILTER  TROUBLES 

In  addition  to  the  oil  or  water  filters  to  take  soot  from  the 
gas  some  recorders  have  other  large  receptacles  filled  with  cotton 
through  which  the  gas  passes  and  is  cleansed.  The  filters  are 
usually  oil  or  water  sealed  to  prevent  air  leaking  in.  Care  must 
be  taken  when  renewing  the  waste  or  whatever  medium  is  used 
in  these  filters,  to  not  pack  it  in  so  tightly  as  to  prevent  the  gas 
going  through  fast  enough.  The  waste  should  not  be  allowed  to 
soak  up  too  much  of  the  liquid  used  in  the  seals,  for  then  the  flow 
of  gas  will  be  needlessly  impeded. 

THE  CO2  CHART 

It  is  common  practice  in  some  plants  to  neglect  putting  on  the 
chart  the  number  of  the  boiler  which  the  chart  is  serving  and  also 
the  name  of  the  fireman  operating  the  boiler.  This  is  very  poor 
practice  for  it  is  not  possible  without  reference  to  time  sheets  to 
tell  what  fireman  produced  a  particular  chart  from  some  particular 
boiler.  The  very  purpose  of  a  CO2  recorder  is  to  act  as  a  check 
on  the  fireman  but  this  purpose  is  defeated  if,  after  the  charts  are 
filed  away,  they  cannot  tell  from  which  boilers  they  were  taken  or 
who  fired  that  boiler.  Never  fail  to  put  on  the  chart  the  date, 
boiler  number  and  name  of  the  fireman,  and  if  there  is  an  unusually 


CO2  RECORDERS  185 

low  record  taken,  find  the  cause  and  write  the  particulars  on  the 
back  of  the  chart. 

With  recorders  using  rectangular  charts  that  are  put  on  a 
cylindrical  drum,  care  should  be  taken  to  get  the  chart  evenly 
fastened  on  the  drum.  Otherwise  the  zero  of  the  chart  will  be 
incorrectly  located  and  the  readings  will  be  wrong.  The  top  edge 
of  the  chart  on  most,  if  not  all  cylindrical  drum  machines  should  be 
even  with  the  top  edge  of  the  drum. 

Usually  a  smeared  chart  will  be  produced  if  more  than  nine 
readings  are  made  per  hour.  About  seven  readings  per  hour  are 
sufficient  for  all  practical  purposes  and  this  number  will  give  a 
neat  appearing  chart.  The  number  of  readings  are  usually  regu- 
lated by  the  size  of  a  stream  of  water  running  from  a  pet-cock. 
It  is,  therefore  important  to  keep  this  water  free  of  dirt  and  par- 
ticles that  might  stop  the  opening  in  the  cock.  The  water  tank 
should  be  well  covered.  This  point  should  be  well  observed  in 
cement  works  plants  and  others  where  the  atmosphere  is  heavily 
laden  with  dust. 


INDEX 


Air,  composition  of,  7 

estimating  supply,  50 
excess  for  combustion  of  fuel,  49 
leaks  in  CO2  recorders,  180 
ratio  of  required  to  supplied,  78 
required  per  pound  combustible, 

16-19 

Alkalinity,  test  for  in  feedwater,  167 
Ash,  and  refuse  in  boiler  test,  142 
calculation  of,  in  boiler  test,  141 
in  coal,  6 

Balance,  for  weighing  coal  samples, 

28-30 

Boiler,    apparatus   for   finding    effi- 
ciency, 131 

efficiency,  formula  for,  130 
horsepower,  117 
test,  ash  and  refuse  in,  142 
duration  of,  136 
evaporation  in,  actual,  146 
form  of  report  for,  137-140 
heat  balance  in,  148-154 
precautions    before    starting, 

135 
starting  and  stopping,  136 

Calcium,  combining  weight  of,  157 
sulphate,  160 

Carbon,  burning  of,  4-12   ' 

consideration  of,  in  boiler  test, 

141 

dioxide,  explained,  14 
estimating  total  in  coal,  74 
in  volatile  matter,  chart,  75 
monoxide,  explained,  14 
oxygen  required  per  pound,  15 

187 


Carbon,  where  found,  2 

Carbonate,    calcium,    formation   of, 

157 
magnesium,    combining    weight 

of,  iS9 

treatment  of,  162-170 
Chimneys,  design,  94 

effect  of  too  large  or  too  small, 
86 

estimating  required  height  of,  99 
Coal,  air  dried,  39 

as  received,  39 

ash  in,  6 

analysis  of,  22-35 

calorimeter,  use  of,  41 

crucible  for  burning  samples,  30 

making  a  proximate  analysis, 
35-40 

moisture  in,  6 

oxygen  in,  6 
Coal  sample,  balance  for  weighing,  28 

burner  for  heating,  30 

grinding  and  preparation  of,  35 

quartering  of,  25 

taking,  24 

volatile  matter  in  dry,  39 

Desiccator,  form  and  function  of,  32 
Draft,  estimating  required,  97 

gages,  location  for,  133 

intensity  of,  formula  for,  92 

measurement  of,  86 

natural,  86 

principle  of,  89 

required  for  different  coals  and 
cobmustion  rates,  97 

temperature  as  applied  to,  87 


188 


INDEX 


Drying  oven,  how  to  make,  33 

Element,  definition  of,  2 
Evaporation,  actual  in  boiler  test, 
146 

equivalent,  117 

factor  of,  117 

Feed  water,  analysis,  proximate,  163 

calcium  carbonate  in,  156 

collecting  sample  of,  167 

common  impurities  in,  156 

temporary  and  permanent  hard- 
ness, 161-169 

test  for  alkalinity  in,  167 

testing  for  acidity  in,  168 

testing  treated,  171 
Flue-gas,  analysis,  49 

apparatus,  best  location  for,  72 
care  of,  71 
required  for  analysis,  49 

checking  results  of  analysis,  64 

collectors,  181 

effect  of  temperature  and  pres- 
sure on  analysis,  60 

solutions  for  CO2,  CO  and  O, 
66-68 

specific  heat,  72 

taking  sample,  68 

testing  for  CO2,  CO  and  0, 63-65 
Fuel,  calculations  of,  in  boiler  test, 
141 

estimating  heat  value,  40,  44,  47 

Gas,  weighing  of,  7 

weight  as  effected  by  tempera- 
ture, 8 

Heat,    absorbed    by    water    during 

boiler  test,  146 
balance,  148-154 
definition  of  unit  of,  10 
lost  in  flue-gases,  72 


Heat,  measurement  of,  9 

of  the  liquid,  114 

production  of,  4 
Horsepower,  boiler,  118 
Hydrocarbons,  forms  of,  23 
Hydrochloric  acid  solution,  166 
Hydrogen,  combustion  of,  5-15 

Indicators,  in  feedwater  analysis,  166 
Latent  heat,  106 

Magnesium,  bicarbonate,  159 

hydroxide,  159 

sulphate,  160 
Moisture,  in  coal,  6-32 

in  steam,  calculation  of,  143 

Nitrogen    estimating    quantity    in 
flue-gases,  76 

Orsat,  care  of,  62 

copper  spirals  for,  54 

emptying  pipettes,  58 

filling  with  water  for  practice,  56 

kinds  of,  51 

loading  with  reagents,  57 

manipulation  of  three-way  cock, 
62 

preparing  for  analysis,  58 

solutions  for,  66 

unpacking  and  assembling,  52 
Oxygen,  in  coal,  6 

solution  for  in  Orsat,  66 

Pressure,  as  influenced  by  altitude, 
in 

gage  and  absolute,  no 
Proximate  analysis,  24 

apparatus  for  coal,  26 

of  feedwater,  163 

Quality  of  steam,  formula  for,  127 


INDEX 


189 


Recorders,  CO2,  advantages  of  mul- 
tiple, 181 

caring  for,  182 

correct  location  of  sample  pipe 
for,  183 

correct  position  of  chart  for,  184 

effect  of  air  leaks,  183 

filters,  184 

renewing  solution,  180 

strength  of  solution,  181 

troubles  of,  180 

Specific  heat  of  flue-gases,  72 
Steam,  calorimeters,  122-127 
formula  for  quality  of,  127 
heat  of,  as  effected  by  quality, 

120 

latent  heat,  106 
moisture  in,  calculating,  144 
properties  of  saturated,  tables, 

109 

quality  of,  120 
saturated,  superheated,  and  wet, 

1 06 

Sulphates,    treatment    of,    in    feed- 
water,  163-170 
Sulphur,  in  coal,  5 

Sulphuric  acid,  use  of,  in  desiccator, 
32 


Temperature,    absolute,    applied    to 

draft,  87 

of  flue-gases,  measuring,  79 
Thermometer,  chemical,  33 
Titrating,  accuracy  in,  166 

Ultimate  analysis,  22 

Volatile  matter,   estimating  carbon 

in,  chart,  75 
definition,  23 
in  dry  coal,  39 

Weight,  combining,  of  elements,  12 
of  COz  by  incomplete  combus- 
tion, 14 

of  gas  as  effected  by  tempera- 
ture, 8 

Water,   alkalinity  of,  167 

boiling  temperatures,  104 
burette  for  measuring,  165 
collecting  samples,  167 
common  impurities  in,  156 
feed,  treatment,  155 
indicators  for  analyzing,  166 
proximate  analysis,  163 
testing  treated,  171 


YC  70300 


331181 


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